I have used Thumbtack, off and on, for a couple years. Here is what I have found:
Fill out your profile as thoroughly as possible. Answer a bunch of the extra questions, add pics, etc.
Don't provide a price, just say you would need to see the property.
In your response make sure to be personable and professional. Emphasize a couple benefits of working with you, and let them know you really hope to be able to work with them. My goal is for my response to be so well crafted that they think, "this guy is probably more expensive, but I would love to work with him".
Don't expect to get a response from more than 1 out of every 4 or 5 leads, at best.
Because of the response rate I have found that a client costs $15-$20 on Thumbtack. So one time mowing or small cleanups doesn't make sense to chase.
Don't assume they are all cost shoppers. Some just don't know how to find a good contractor, or have filled out contact forms on 4 of your competitor's sites, got no response, and now are desperate. (I have actually used it that way myself for a parking lot resurfacing job).
Hope that helps!