I gave this advice to a couple of people in my chess club:
'Meaning no offense, but I noticed a few missed tactics in your game.
It isn't just a matter of tactical skill. No one at our level has the skill to see all tactics. What I have noticed is that Class A players usually have a "spidy sense" to know which positions could possibly have a tactic. They may not see the tactic right away, but they know that there could be a tactic in the position, so they analyze deeper. Usually this means that something is out of balance, like a exposed king, or a loose piece, or the position just doesn't feel right. This is when you know to give it a second look.
Developing this "spidy sense" can help you bring up your rapid game, possibly by a lot. '