Actually, since you always have a couple of at-will options, and half or more of your attack powers are encounter powers, I've discovered that you can in fact get through fights without using your dailies. Unfortunately, saving your daily powers only helps if you eventually get to use them, so the best rule of thumb is to wait until you see a moment where your daily would be cool, and then go for it.

Definitely if you are about to spend an action point, consider using a daily ability that round. Especially if you have a tactical warlord around, or you are a human or half-elf with action surge.