1) Word of mouth is the most powerful way to win clients. When someone says "I know a guy that..." and that guy is you, you win, there's no competition.

2) You do really great work to those clients and some of them will tell "I know a guy that..." to someone else.

3) Repeat.

Now, this is how you get more freelance projects. At some point you will ask, "How do I get better clients?". But that's another question.