Back to Basics: Endgame Theory

My endgame something I really need to work on(as well as other aspects of my game but I am trying to take a moment to focus on my end game). 

I have a list of books that I plan on getting in time and I know of ways to get end game positions to study and practice on.  

What is a basic breakdown of the endgame theory as a whole?

Are you talking about basic endgame principles?

Passed pawns must be pushed

Push the unopposed pawn

Centralize the king

Place your pawns on the same color squares as your opponents bishop

That kind of stuff?

Yes.

Besides the ones i mentioned:

Play "Backwards-to-Forwards" Chess

Prnciple of 2 weaknesses

Use your pawn majority - create a passed pawn

There are others, but that should get you started

Keep in mind these are "principles" Trying to win endgames on principles alone will not get you very far, unlike openings where you can get through an opening with Open Principles. 

Some more chess endgame principles:

1. Get your king close to the action – ideally in front of your own pawns.
2. Cut the enemy king off from the action when you can.
3. Rooks should be placed behind passed pawns – your pawns or your opponent’s pawns.
4. Advance your good pawns to increase your chances of creating a passed pawn.
5. Attack your opponents weak pawns to force your opponent’s pieces into defensive positions.
6. Place your pieces on squares where they restrict the mobility of your opponents pieces.
7. If you have a material advantage, it is good to exchange pieces but keep pawns. Exchanging pawns increases your opponent’s drawing chances. The less pieces there are on the board, the more important the pawns become.
8. If you have an advantage, you should leave pawns on both sides of the board so that your opponent will be forced to defend on both sides of the board.
9. If you have one bishop, put your pawns on the opposite colour squares – this way you can control squares with your pawns which the bishop can’t control.
10. The bishop pair (two bishops) are usually very powerful in the endgame, possibly worth at least an extra pawn.
11. The best piece to block a pawn with is a knight. This is because the knight also attacks the squares from where other pawns can protect the blocked pawn.
12. Passed pawns should be pushed forward and supported by all your pieces. Remember – promoting a pawn can often be as good as checkmate since you will be able to force a win with a new queen.
13. Passed pawns on the edge of the board is a key advantage since you can use it to distract your opponent’s pieces (or king) away from other targets.
14. A bishop is usually slightly better than a knight when the action is on both sides of the board. However, when the pawns are only on one side of the board, the knight can be more useful since it can reach both the light and dark squares.
15. Bishops on opposite colour squares tends to often lead to a draw even when one player has an extra pawn or two.
16. Create threats on both sides of the board. This may cause your opponent’s pieces to become overloaded with defensive tasks and give you an opportunity to promote a pawn by a tactical combination.

 I would recommend doing something most people are not willing to do, because it involves work.

That is to get a copy of Rueben Fine's book " Basic Chess Endings" & read & play through every diagramn in the book cover to cover.

If you have any energy left after that, read & play through anything by C.J.S. Purdy.

Thanks everyone for the advice!  I really appreciate it!

Should you trade rooks in the endgame?

 @arun - To the extent that there is a principle about exchanging rooks, you should exchange rooks if you have advantage and are trying to win. If you are trying not to lose, you should keep rooks on the board.  This is obviously not always true so please people do not post positions in which this general rule doesn't apply.  The place this comes up most is R + x P's v R + (x - 1) P's.  It is almost always much easier to win if you can take the rooks off the board.  In fact, a key theme in these endings is that exchanging rooks is a threat the superior side can use to advance a pawn.  But a position like each side has 3 pawns on their original files on the kingside but white has a queen rook pawn is almost always an easy win when there are no rooks and a (hard to get but theoretical) draw with rooks usually.  

One good principle, if you and your opponent each have a minor piece, and a rook:

If you are trying to draw, trade the minors.

If you are trying to win, trade the rooks.

(Which goes back to the old adage, "all rook endgames are drawn")

One for opposite-colored bishops:

If you want to draw, put your pawns on the color of your bishop.

If you want to win, put your pawns on the color of your opponent's bishop.

If you want to win, trade pieces, not pawns.

If you want to draw, trade pawns, not pieces.

"... The only real problems with [Basic Chess Endings] are the errors and the fact that it is now very dated. ... the book is now in algebraic notation and the layout has in some ways been improved. ... Perhaps the greatest disappointment ... lay in the failure to correct many of the errors in Fine's book. ... I don't think it is acceptable in the 21st century to produce an endgame book without computer- and database-checking. ... the book can be recommended for Fine's groundbreaking general explanations. Just don't expect complete accuracy or up-to-date endgame theory." - GM John Nunn (2006)

Various endgame study possibilities discussed at:
https://web.archive.org/web/20140708103149/http://www.chesscafe.com/text/review594.pdf
https://web.archive.org/web/20140708105702/http://www.chesscafe.com/text/review645.pdf

https://www.newinchess.com/media/wysiwyg/product_pdf/9026.pdf
https://web.archive.org/web/20140708234309/http://www.chesscafe.com/text/review704.pdf
http://www.gambitbooks.com/pdfs/Understanding_Chess_Endgames.pdf
https://chessbookreviews.wordpress.com/tag/chess-endgames-for-kids/
http://www.gambitbooks.com/pdfs/Chess_Endgames_for_Kids.pdf
http://theweekinchess.com/john-watson-reviews/endings-endings-endings
http://theweekinchess.com/john-watson-reviews/the-end-game-comes-before-we-know-it
http://theweekinchess.com/john-watson-reviews/theres-an-end-to-it-all
Before buying any particular book, I suggest going to the publisher site to see if it is possible to view a sample.

One thing I forgot to metion earlier, if you never, ever bother to learn anything about the Endgame, the rest of your life, KNOW THE OPPOSITION!!

If not, there are plenty of good reference tools on Chess.com, or the internet in general, dedicated to the opposition.

Know it. Back to front, Inside, and out. Practice it until you don't need to even think about it anymore. Make sure your hand will perform the proper technique to win, or draw, this position.

Every time I am studying a game and reach such a position in a side variation, I stop and follow it through to the end, until the pawn promotes, or stalemate occurs.

The last thing you want is to be sitting across the board from some 8 year-old kid, with seconds on your clock, and need to think "What was that move order again? I think it starts with..... oh my flag fell! Good game!"

How do you win the king vs the king and two bishop endgame.