1. your site should have a very simple, tree-like structure
2. your visitors should get to the product page in 3 or less clicks
3. you don't want to have tons of links of product pages on your main page, see #1
4. the more pages with unique content you have - the better
5. the bigger the page - the slower the loading speed. Keep that in mind, you want as fast loading pages as possible.
6. for the rest - use common sense. Imagine you are a visitor of your website. Do you like what you see?