Hi @omar120 and welcome to the forums.
We’ve had several recent articles and discussions on this very subject. I suggest you take a look at these, and if you have further questions, join in the discussions on the topics.
http://www.sitepoint.com/6-strategies-freelancers-win-from-agencies/
http://www.sitepoint.com/community/t/what-i-wish-id-known-3-years-ago-about-freelancing/115450/10