Hi @WorldTrav - welcome to the wonderful world of pet & house sitting. The first sit will always be the most difficult to get but at the moment there are more sits advertised than sitters available which will really improve your chances.
The number one important thing is that you need to start you collection of reviews. As time goes on these come naturally, and gradually as each sit ends but to start you need to give them a bit of a boost! To do this think about doing a couple of very short sits, 1 or 2 days is a great way to instantly get yourself some reviews. Staying local so that you are not incurring travel costs is a good idea initially.
Once you have a couple of reviews under your belt then you will find it much easier getting accepted for the sits that you really want to do - good luck.
You may find having a look through this thread helpful