Hi ! Your design need lot of improvements before to be accepted on Themeforest…Compare you item with -> http://themeforest.net/popular_item/by_category?category=wordpress (Spacings, colors, fonts, originality, shadows…) You have to look at the basics and then we could be more specific… It’s just my personal opinion, best regards F²
You should work on the navigation bar… the font and it’s size are awful. Also, you should try to change the sidebar style, and those gradients… the footer it’s very bad styled… try changing the font to a custom one… good luck !
That is no design… that is some stuff put together to form a theme + some ugly colors. First thing you need to do is to reach to a good design on paper/photoshop/fireworks or whatever.graphical.form.you.prefer… after you have that you can start coding.