Come on Markster, they write whole books about each and every one of your questions. I'm not blowing you off, it's just too broad a series of questions. Lucky you though, chess.com has study plans designed to inspire inquisitive minds like yours. I think you can learn a lot even if all the resources listed aren't available to you. Best of luck.
http://www.chess.com/article/view/study-plan-directory
Hey everyone
I'm an intermediate playing high school chess, and I just quickly wanted to ask if the more experienced players could give me some general guidelines for middle game play especially. What should I look for? When should I push pawns? When should I exchange? Stuff like that. Any help would be most appreciated. Thanks in advance!! :D