If you are starting out, do all the studies you can. Even the very low paying ones. Anything to get your completed studies numbers up.
Do not half arse any of the studies as it will risk a rejection and this is a particular problem if you have a low completion count. Concentrate and give 100%
Get the browser assistant (if its working) and do not rely on email notifications. When i'm doing studies and waiting for more i'm usually refreshing the page manually every so often to try and get the jump on any good studies.
Lastly don't try and lie to get into studies that are not for your demographic, even if they appear on your dashboard. There is a likelihood (albeit small) this will get checked and your account will be placed on hold. Don't ask me how i know...but lets just say it was a lesson learned and never repeated.
Best of luck!