Spend some time reading through the forums here...just about everyone reports a really low score in the 500s on a Kaplan test and then has no idea what to do. The Kaplan tests are nothing like the real thing. Take a GMATPrep test (official test) or a Princeton Review test for a much better idea of your starting point.

There are also several great posts, some of which should be "sticky" posts at the top of the forum, about how to prep. But don't make any decisions about your prep based on a Kaplan score! You're probably not nearly as bad off as you think.

the above advice is good. Also, it's good to think about making some sort of schedule/goal to study with as well as possibly taking class if you have the time/money. Classes are a good way to force yourself to study harder and does give some shortcuts that otherwise may take some time. But websites like this is very good as a resource for studying tips. Lots of people improve, so don't worry!