depends on the mood and the person...
videos are relaxing (see the other thread with chesslectures.com, or chessbase videos)...
books are probably best in case you have a strong will(and you can find many really good)...
ctart software is nice for tactics, but you can solfe tactic problems also from books or internet
1-2 lessons with a titled player where you can show him some of your games and he can point you where to focus to improve
1500 rating here ? tactics tactics tactics(Go get GM Alburt chess book Chess Training Pocket book...it is a tactic book, or just solve chess tactics problems...you can find many everywhere)