Hard not to agree with smallcompany's list and chewy's suggestions. To #11 I would add that you should periodically look at your successful keywords and try to come up with new variations.
Maybe it does not apply if you do a lot of brand/product specific campaigns (I do lead generation with a lot of generic terms), but as an example let's say I have a successful keyword in [beautiful dresses].
I've had kind of weird variations like [beautiful com] and [beaufitul net] produce leads, running with the same ad as [beautiful dresses]. Never be afraid to test weird (and often very cheap) keywords!