The problem with your question is that it depends on too many variables to give you a specific answer:
What's the target market?
Who's competing in that target market?
What is your overhead?
How effective is your advertising?
Do you have issues that may be interfering with the usability and profitability of your site?
Is your code clean?
Have you participated in any schemes designed solely to manipulate search engines?
Those are just a few that come to mind off the top of my head.
