Good questions ... for your first question, I'd point you to NM Dan Heisman's book recommendations which are arranged by rating levels:
http://danheisman.home.comcast.net/~danheisman/Events_Books/General_Book_Guide.htm
His Chess Cafe Novice Nook articles are worth their weight in gold ... so make sure you read those too!
How do you study? Depends on how you efficiently absorb information to the point of actually "using/applying" it in your games.
What would be ideal => You study X pages of new information, play enough slow time-control chess games to use X in your own games ... rinse and repeat.
The key is to find the exact mix of study + slow game play to see an increase in your playing strength.
Too much studying without actual practice leaves you quickly forgetting or misapplying what you learned (overload of information, lack of context to actually apply what you've learned) and often leads to frustration (I have read 100 books, why am I still a ____ rated player). My former coach says this is akin to a 2-3rd grade student struggling with basic math but whining that he can't do calculus as well as the high school students.
Once again, we're all "different" and learn in different ways. I have a notoriously bad memory so I tend to keep my own notes and journal up instructional positions I come across so that I can review them later. Sometimes re-reviewing something 3-4 times and getting to apply it in an actual game is the only way stuff actually cements itself into my "long term" chess knowledge.
One other key ingredient to this "Study + Practice" mix is having your lost games critiqued by stronger players. You'll get some good advice in these forums if you post those games and the stronger players (who are decent!) will quickly spot "bad chess habits" you currently have.
A lot of relatively new players get into this defensive state of denial when told that a review of their own games offer the best chess lessons money could buy. Now to a Master's eyes, you're probably making 10-20 mistakes (some subtle, some glaringly obvious) per game. Can you fix them all? In time ... though you'll probably be sweeping the bigger pieces of broken glass from your kitchen floor before you go after the tinier pieces. So it's quite instructional to hear a stronger player looking at your game say "Well, I would never play a move like that because of ...." . As much as I've read books in the past, most of my own chess playing skills came from being yelled at to "NOT" do something ... that's a whole lot easier to remember than it is to actually learn to do something you never thought of doing. A constant critique of your games can be very helpful as part of your study program.
Can anyone recommend any good chess books for players rated between 1200 and 1700? Most books that I've seen are for more advanced players. Also ,have you actually read and /or studied the books? Have they helped your game? Next,how does one study? Not what should one study, but how. Thanks for any input.