Maybe I'm speaking blasphemy, but I think there is something even more important than tactics:
I'm still a firm believer that studying tactics is the number one thing someone at my rating can do to improve their chess rating away from the board.
But once I'm at the board, the best thing I can do is apply a rigorous thought process every single move.
This is something that Dan Heisman refers to frequently in his columns and books. He calls it playing Real Chess.
Two games from my last tournament games I lost pieces - not to tricky four-move combinations, but just by simply hanging a piece!
So my new quest involves two points to focus on:
1. The best thing to do away from the board = tactics.
2. The best thing to do at the board = thought process.