It depends how long your site has been going. In my limited experience it has taken three months for Google to start sending me decent traffic.
Yahoo and others take months to index. I submitted my site to Yahoo in early December, and I haven't had one visitor via them yet.
The best things I can suggest for increasing traffic...
1. Make sure you have original content. Google doesn't like copied product descriptions. I saw a visible rise after I changed most of mine.
2. Make sure you include relevant keywords in your product description copy, a good rule is twice at the start and once at the end of a product description of 50 to 100 words.
3. Create incoming links from blogs, forums and articles. With keyword-rich anchor text, and linking to relevant pages directly.
4. Target the people you're looking for. Don't only post in dofollow pages to gain the Google attention. A great example of this is I joined a forum devoted to male enhancement

and that is now the leading source of traffic for my site over and above everything else.