Since you are applying in a very popular location, you are going to have a lot of competition. I think you need to get more experience before applying to popular sits. Try to get some short sits near where you live so you can build up your references. Look for last minute sits. Those sits are more willing to take a chance on someone with no or few reviews. Do an amazing job at those sits so you get rave reviews!
Also your application message is very important. Search this forum for discussions about application messages. Here is a good one: The perfect application?