Blundering

use the computer as a blunder checker (if everything seems fine and all of a sudden the engine makes a dramatic jump then someone blundered- look at it and try to figure it out- use computer if you get stuck to go over the line/variation
it helps if you can really limit your games to put as much mental focus in your moves so when you do blunder you can immediately recall the “reasons” you made a move-
my most common “blunders” when i am concentrating is usually not noticing opponents threats and/or just technically not executing properly
then it is a matter of going over the specific positions in my games to see the failures and to register them and the lessons they teach in the “pattern recognition” bank
i think it helped me to focus on overprotection as a goal in my games when i was trying to make a point to improve; seeing loose pieces in my position and getting it “fixed” if i can and really trying to visualize how a certain move or candidate move affects the whole picture
it is not easy and i still struggle mightily but you have to be hard on yourself and not let yourself off the hook when you make a catastrophic blunder

just study basic tactics like pins forks back rank mates... do 1 to 3 move puzzles... even if it seems simple and repetitive it will help you from making mistakes... we all hang pieces from time to time but try not to make it habitual... I think it's pretty obvious you just need to sharpen your tactical vision

These will help lessen your blunders
Learn the different tactical themes like pin,fork,skewer, double attack,discovery etc.
Learn checkmate patterns.
Solve tactics problems.
Always study your opponent's last move.
Always look at the whole board.
"... thinking correctly in most positions takes time. Playing almost exclusively fast games obviously precludes practicing correctly, and so you will never get very good! Sure, fast games are fine for practicing openings (not the most important part of the game for most players) and possibly developing decent board vision and tactical 'shots', but the kind of thinking it takes to plan, evaluate, play long endgames, and find deep combinations is just not possible in quick chess. … for serious improvement ... consistently play many slow games to practice good thinking habits. ... I know that a large percentage of my readers almost exclusively play on the internet - after all, you are reading this on the internet, right!? But there is a strong case for at least augmenting internet play with some OTB play, whether in a club or, better yet, a tournament. Tournament play gives you the kind of concentrated, slow chess that often helps improve your game, especially if you are inexperienced at slow play. I would guess that players who have never played OTB usually gain 50-100 points of playing strength just from competing in their first long weekend tournament, assuming they play five or more rounds of very slow chess. ... Sure, an occasional weekend event takes a lot more of your time, but the benefits are comparatively greater if improvement is your ultimate goal. Don't have two day? Try a one-day quad (a round-robin among four similarly rated players). How often should you play? ... A minimum of 8 OTB tournaments and about 100 slow games a year is a reasonable foundation for ongoing improvement. ... Can't make 100? Then try for 60. If you only play three or fewer tournaments a year and do not play slow chess regularly at a club (or on-line, where G/90 and slower play is relatively rare), then do not be surprised that you are not really improving. ..." - NM Dan Heisman (2002)
https://web.archive.org/web/20140627052239/http://www.chesscafe.com/text/heisman16.pdf

You have terrible openings, but that is not why you lose. You lose because you are trying for tactics that are easy to defend against. Sometimes you get the upper hand and you win a piece or two, however, you do not have the technique to win the game because often times in those situations where you do find a material advantage your opponent finds counterplay and checkmates you regardless. In all the cases there was a way to defend against your opponent's threats, however, it seems you are not looking at what the last move did to the position because you lose often times right when your opponent makes a simple threat that you do not parry and simply lose because of it.
Unless you spend at least some time on openings, you will often play games where you will be down a pawn or two or even a piece in the opening. As your rating increases, you will have to continually spend more time on your opening prep to combat this. I'm guilty of the same thing myself. I just recently lost a game because the guy played a move out of the book and I didn't know what to do. I gather most people know my repertoire training book and avoid the methods in the book I am going over just to throw a curveball. One thing for sure is that will not happen again. That's how you improve. Correct your mistakes, and try again. Same as anything else.
I would recommend you start by just doing 15 tactics a day and work your way up from there until you are doing about an hour of tactics. Don't rush to get to the hour! Slowly get there. I am starting again myself.
Get a good annotated book on games and study one master game a day.
Play one slow game a day and apply the thinking method given to you by bacon.
If you do that in about a couple months you should get to 1200 easily.
Oh, you have to analyze your games after you play.
Also, find time to play some blitz games for opening practice. There isn't a specified amount that you should do. Just do enough that you have time for, and enough that will challenge you. If you are not challenged, you will not improve.
Eventually, if you go over your openings by cross-referencing your game with what mastered played in that position, and reject the openings you don't want and assimilate the openings you do, you will have your very own opening repertoire in a matter of time. Thing is though you will not have a master telling you which openings to go for. So you are on your own in that department, however, you could just buy a repertoire book. Easy enough, trouble is you will still have to look up games in those openings you get the feel for the type of game that opening creates.
All of this takes time. Time, which most people do not have. That is why you really have to ask yourself, "Do I really want to get better," and answer the "Why?" part of it too.
You will also have to spend some time on endgame.
"... for those that want to be as good as they can be, they'll have to work hard.
Play opponents who are better than you … . Learn basic endgames. Create a simple opening repertoire (understanding the moves are far more important than memorizing them). Study tactics. And pick up tons of patterns. That’s the drumbeat of success. ..." - IM Jeremy Silman (December 27, 2018)
https://www.chess.com/article/view/little-things-that-help-your-game
https://www.chess.com/article/view/how-to-start-out-in-chess
https://www.chess.com/news/view/a-new-years-resolution-improve-your-chess-with-new-lessons
"... In order to maximize the benefits of [theory and practice], these two should be approached in a balanced manner. ... Play as many slow games (60 5 or preferably slower) as possible, ... The other side of improvement is theory. ... This can be reading books, taking lessons, watching videos, doing problems on software, etc. ..." - NM Dan Heisman (2002)
https://web.archive.org/web/20140627084053/http://www.chesscafe.com/text/heisman19.pdf
"... If it’s instruction, you look for an author that addresses players at your level (buying something that’s too advanced won’t help you at all). This means that a classic book that is revered by many people might not be useful for you. ..." - IM Jeremy Silman (2015)
https://www.chess.com/article/view/the-best-chess-books-ever
Here are some reading possibilities that I often mention:
Simple Attacking Plans by Fred Wilson (2012)
https://web.archive.org/web/20140708090402/http://www.chesscafe.com/text/review874.pdf
http://dev.jeremysilman.com/shop/pc/Simple-Attacking-Plans-77p3731.htm
Logical Chess: Move by Move by Irving Chernev (1957)
https://web.archive.org/web/20140708104437/http://www.chesscafe.com/text/logichess.pdf
The Most Instructive Games of Chess Ever Played by Irving Chernev (1965)
https://chessbookreviews.wordpress.com/tag/most-instructive-games-of-chess-ever-played/
Winning Chess by Irving Chernev and Fred Reinfeld (1948)
https://web.archive.org/web/20140708093415/http://www.chesscafe.com/text/review919.pdf
Back to Basics: Tactics by Dan Heisman (2007)
https://web.archive.org/web/20140708233537/http://www.chesscafe.com/text/review585.pdf
https://www.chess.com/article/view/book-review-back-to-basics-tactics
https://static1.squarespace.com/static/5856bd64ff7c50433c3803db/t/5895fc0ca5790af7895297e4/1486224396755/btbtactics2excerpt.pdf
Discovering Chess Openings by GM John Emms (2006)
https://web.archive.org/web/20140627114655/http://www.chesscafe.com/text/hansen91.pdf
Openings for Amateurs by Pete Tamburro (2014)
http://kenilworthian.blogspot.com/2014/05/review-of-pete-tamburros-openings-for.html
https://chessbookreviews.wordpress.com/tag/openings-for-amateurs/
https://www.mongoosepress.com/catalog/excerpts/openings_amateurs.pdf
Chess Endgames for Kids by Karsten Müller (2015)
https://chessbookreviews.wordpress.com/tag/chess-endgames-for-kids/
http://www.gambitbooks.com/pdfs/Chess_Endgames_for_Kids.pdf
A Guide to Chess Improvement by Dan Heisman (2010)
https://web.archive.org/web/20140708105628/http://www.chesscafe.com/text/review781.pdf
Studying Chess Made Easy by Andrew Soltis (2009)
https://web.archive.org/web/20140708090448/http://www.chesscafe.com/text/review750.pdf
Seirawan stuff:
http://seagaard.dk/review/eng/bo_beginner/ev_winning_chess.asp?KATID=BO&ID=BO-Beginner
http://www.nystar.com/tamarkin/review1.htm
https://web.archive.org/web/20140627132508/http://www.chesscafe.com/text/hansen173.pdf
https://www.chess.com/article/view/book-review-winning-chess-endings
https://web.archive.org/web/20140708092617/http://www.chesscafe.com/text/review560.pdf

I'm a low rated player, slowly climbing. It seems like there are some clear stages of development in blunders avoidance.
1. Recognizing hanging pieces/exchanges and avoiding/punishing them
2. Recognizing checks, possible responses to checks, and hanging pieces following those respones and avoiding/punishing them
3. Recognizing fork, pin, and skewer possibilities and avoiding/punishing them. (Skewer is kind of part of #2.)
4. Recognizing traps (this is not one you can master, only improve on. Starting by identifying when every response to a move leads to a haning piece/exchange and preparing for/ guarding against the move)
5. Combinations of the above, e.g. a check which forces a fork possibility.
I miss all of these sometimes, and this list ingnores opening and positional priciples. But if you can manage the checklist above then you'll be saying "how did this position happen" and not "why did i do that" when you lose.

Hello, if you like, we can learn chess by skype for free. I have a lot of chess puzzles and chess videos on English.

I find it easier to not blunder when I study my opponents moves instead of looking to attack myself, I try and see where the logical place he wants to move a piece and then try and stop his piece from getting to where it wants to go, if I see him setting up an attack I try and trade pieces he is using for an attack, things like that, also never just instantly react to a move your opponent does, look at it for a little while first, playing to fast is the worst culprit as far as blundering