Visit a few forums and become a regular there. Given time you should be able to post adverts in specific sections. Given time if you're active you can build yourself a reputation to help you increase sales.
You need to find and play with (track) different sites. Find what converts best for you, try all types of marketing and push the ones that really work out.
Forum market place is the best place to post your hosting ads. You can check out some good forum lists, and register there, make some posts and then you can post your ads in the market place section of the forums.