> Do this skill comes to then by trainning or by just memorising the chess variations?
Masters know their pet lines by heart, but they will also choose reasonably good moves in new positions. How someone trains after reaching the master level is not necessarily how you should train if you're far away from it.
> According to one of my mentor, middlegame is all about how to play the sweker,pin,fork and etc.Is there anything more in middlegame?
It depends on your level. If you're 1450 or below, I agree. If you're 1750 or above, I disagree. In-between, I've seen reasonable people argue.
> How to improve these skills?
Post a couple of your losses and your FIDE rating if you have one. Without those, it's impossible to accurately recommend books, software, etc. for you.
High level chess basically involve perfect development in the opening.The players really know where to place thier pieces in the correct squares.Do this skill comes to then by trainning or by just memorising the chess variations?How do they train to improve this skill?How do high level chess players train thier tactics and strategies in chess?Do they study completely the grandmaster games ?Or they solve great number of chess puzzles for this?According to one of my mentor,middlegame is all about how to play the sweker,pin,fork and etc.Is there anything more in middlegame?How to seek for chess principles ?How does high level chess players train thier endgame play?How to improve these skills?
PLEASE HELP ME !!!