how to improve design of my wordpres site?

I saw your site – very nice. The only suggestion I have is to put a little more space between the content and the sidebars via css. Maybe make the text a little smaller.

Have you checked your site for errors? There are quite a few of them. Also, have you submitted your sitemap to the search engines? I don’t know of any plugin that will provide more visitors – I only know of SEO techniques.