Here are 2 tips :
Amazon is both a search engine and a social site.
Search Engine:
Right now i have two fiction books. I can verify that my book with the more popular keyword (also used in the description and tag) sells at a fairly steady rate. Yes, I come up on the front page of Amazon search for it.
My book with the much less popular keyword is a dog. (working on that). I actually come up 2nd on Amazon search for that one - higher than the more popular one.
Q: How do I know which keyword is more/less popular?
A: Google keywords tool, silly!
Social Site:
Don't ignore the impact of reviews, listmania lists, wishlists, etc. This works like any other social /web 2.0 site.
Now it's hard to gain traction so you are going to have to be social here.
Amazon is getting very tough on paid reviews. It shouldn't be that hard to get some friends to buy/read/review your books though. It was hard for me to start asking, but a couple of my friends were really excited about helping. It was asking a lot to get them to purchase, read, and review. That is time consuming. But some people get excited about being part of a book.
Once you get it started, you should get the momentum to get some stranger reviews. Not all of them will be positive, but actually book reviews don't even look real - IMO - if everybody is a fan. I am actually pleasantly surprised with the fact that people took the time to read my book and leave any reviews.
Develop a thick skin and keep going. Look at popular, best selling book reviews. They run the gamut. Besides, it is obvious that there are trolls on Amazon today shooting down competition.
My worst review came from a reviewer who has never left a positive review. But this person still gave me social juice and you know what they say about bad publicity being better than none.