Make sure customers land on the most appropriate landing page for their search. You should probably consider this when designing adgroups, though it is possible to have different links for all of your kwords. If I'm looking for apples, preferably I want to see apples within one click. More clicks = less $.
If possible track kwords, some kwords with great ctr also have horrible roi.
Hope this is useful, possibly you're aware of these tips already. Others here may have more ideas, some quite possibly contradictory to my own which is OK. This is just what works for me and I'm no master, but I do make a good living from adwords and enjoy the lifestyle it allows me ie. more time with family & working on less financially rewarding (though still rewarding) music career.
Hang in there. Good luck with your endeavours.