I have made an opencart theme which is ready to published but i have no idea from where i should start the marketing of site.So any of the suggestion will be very helpful This is the site if some one want to take a look Demos:http://cartthemes.net/Demos/ Download:http://cartthemes.net/?p=62
I made a few sites and used Fiverr to start marketing campaigns for each site. One site I have is selling a book I authored and I found some good gigs for promoting it. Good luck.
I would agree with SoftDev, if you have some extra money I would try doing a PPC campaign first with multiple ads to see what customers are clicking on and what they are paying for. Then you can focus your site on those attributes and do more SEO.
I would mix SEO and PPC, Use PPC to guarantee that you'll have atleast SOME money coming in each month and use SEO for the long haul to increase your overall money thats coming in every month.
If you have a budget then go with PPC campaigns through popular/powerful advertising networks like Google Adwrods, Adbrite Exhange etc. If you don't have a budget, try Linkreferral advertising network where you don't need to spend single dollar (it's a free service).