I have had much success using Thumtack. I've gotten the most responses after tweeking my profile information to sound more friendly, and rewording my templates to suit each situation. I often start with one of my templates, and then add or change it to fit whatever information the potental client has given.
I am a photographer, so I also attach a file with more information about my business and sample photos for whatever type of photos they are looking for. I think that added bonus shows that I am a qualified professional, with experience.
I think creating a strong profile is important. I have read all the questions on my profile and answered them in complete sentences. Think of it from a clients' prospective and how they would see your answers. Also, I try to respond to customer's requests as soon as possible and when I do, I ask open ended questions to keep conversation going. Ex: Do you have any questions I can answer? Another tip is reveiws. Customers want to see someone with the best reviews so if you can get many, they will probably hire you. My clients tell me they have chosen me because I had the "best" reveiws.
If I bid on a project and the poster replies, I try to get back to them as fast as possible. I am always genuine and clear up front about what I can and can not do- this way nobody gets any unwanted surprises. I ask people to look at my website so they can get an idea of my work. If I see they are really interested, I'll propose a price- and if they are still onboard, I'll make them a free sample before I ask for any money. It's the best I can do.