Here is something a little different. You're playing the Black pieces. White threatens your h5 rook with his bishop. Think offense before defense; find the kernel of a discovery. Your rook is aimed at the enemy king and masked by the pawns on h4 and h2. You study the king’s position and see that its only flight square (g1) is sealed off by your bishop. Play on the h-file might be indicated, but how? There isn't yet any way for the pawn on h4 to vacate the file, and then there still would be a White pawn on h2. Both problems would be cleared up, however, if the h2 pawn could be goaded onto g3; then it would be out of the way and the Black pawn on h4 would have something to capture. So plant a piece vulnerable to the pawn on h2, and do it with a threat: Ng3+, a fork of bishop, rook, and king. (If that line of reasoning was too cumbersome, try a simpler one: examine any checks you can give and arrive at Ng3.)
So now consider White's replies. If he plays QxN, fine; Black has h4xQ. But what if White replies h2xN? Black plays the discovered check h4xg3. It isn't quite mate because White still has BxR. But now look for Black’s next possible check. It’s Qh4—and this time it is mate, since Black’s bishop still seals off the king’s only flight square. It’s a lesson in the importance of noting how all of your pieces bear on a position and might be brought into the fray. The queen’s path from its starting square to the side of the board (and thus down the h-file) is a potent resource.