My site was doing pretty well and the traffic had almost reached 700 visitors per day. But one fine day it came down to 400. Since then it has remained between 350-430. I don't know what has gone wrong. I have been doing social bookmarking, article submission, blogs, forums, link submission, FB and following keywords. What more can I do?
Your techniques are good but I suggest you change the content of your site , take participate in Yahoo answers, try business listing , classifieds posting , Follow twitter . Hopefully it will help to generate more traffic .
Re-write some fresh & informative content with Seo criteria link H1 tag image Alt Tag and key word density 2% to 6% and do offpage work post your site on dofollow site.