i see many good ideas here especially the poster who recommended studying tarrasch's ideas.
i agree with andrei_vine that silman is just a lot of bullcrap. yet a lot of people swear by him. my coach insists that silman is even better then kotov and my coach is a brilliant player, being capable of playing 8 games simultaneously blindfolded!
i am personally still undecided about silman. personally i like gufeld's chess strategy. but i still have a nagging feeling that i need to perfect the basics first!
i think at one point of time karpov was asked how one should train at chess and he said not to forget the classics-nimzowitsch, tarrasch, capablanca, alekhine.
my personal favorite player is alekhine.
Player longer time control games to start. Dedicate some time each day to study the game, dividing the time between opening, middle and endgame studies. Go through your opening. Are each of your opening moves adhering to good opening principles. Play for development rather than fast attacks. In the middle game try to move your pieces to more active squares before launching an attack. Most players at your level are not good at closed positions so use that to your advantage. Play through as many endgames as possible. Balance study with actual play. Repeat, do not play fast games. While Blitz is fun, it can actually reinforce bad habits. Study master level games. Watch videos, especially those of IM Andrew Martin, who provides great explanations to every move made in the game!