First World Correspondence chess champion and popular author C.J.S.Purdy recommended going over master games and trying to guess the move as a fast way of improving.

ChessRater includes a collection of 40 classic master games in which you try and guess the winner's moves. It is something like "How good is your chess?", but multiple choice. You are given a rating per game and brief reasons behind each move.

Watch your rating grow with practice.