Don't even attempt these until you can solve the hard puzzles most of the time!

 

You should definitely set these up at the board and work on them without moving the pieces. Ideally you should write your key variations down. When you really feel you can't get any further like that you can start moving the pieces to analyse.

 

Some of these are traditional puzzles with one clear best answer. Others are hard calculation practice where there is more than one good way of proceeding.

 

Don't worry if you can't solve them. Even trying to will improve your calculation if you work hard at them.