If you just join a Chamber and do nothing, you will only get referrals by accident.  You must become active with the Chamber of Commerce and attend as many events as you can so that other members get to know you and understand that you are making a commitment to the Chamber. 

Look closely at the events offered by the Chamber to see if the clients that you are looking for are attending.  Go to those events, even if there is an extra charge.

Remember don't act like a dog running around and jumping on everyone.  Talk to 4-5 new people per hour and talk about their businesses more that you talk about yours.  You want to develop a relationship with members.  Remember that although they may become a client, you are looking to be referred to the 100-200 people that they know.