Do couple of small sites for free. Also start giving free demo website/ sample sites to clients. If they don't buy, well you can add to your portfolio to show it to other clients.
In no time you will have lot of sample sites u can start showing to prospective customers and your conversion rate will increase. And slowing afterwards you can stop giving away free sample demo sites etc
Once you are established ... My only advice would be :
Over the time one thing I Learnt; never work without a deposit, once u ask for a deposit first, the bogus client would disappear in no time!!
Getting stated is imp.... Once the ball starts rolling its on u....