Jakob Nielsen‘s has been writing about the what things you can do to make more money.
1. Email Newsletters, 2. Informative Product Pages, 3. High-Quality Photography, 4. Product Differentiation and Comparisons, 5. Support for Reordering, 6. Simplified Text, 7. Catering to Seniors, 8. Gift-Giving Support, 9. Search, 10. User Testing.
The high-ROI ideas I have highlighted here have one thing in common: they add value to your site by enhancing its value for customers. That is, they give users what they want and need.