The number one reason why I click away from a site is layout. The front page should be set up so that I can easily find what I am looking for. If it is "too busy" I tend to scroll a bit, but if I don't find what I am looking for, I move on. Unless it is the only site (unlikely anymore) that provides what I am looking for.
Colors should correspond to the content/product you are selling/promoting. If you haven't already done so, look up some of the research on colors and their effects on sales.
Ease of navigation is another thing. Links to pages that then provide links to what I am actually looking for is irritating.
My 2 cents.