You could start by taking an MCAT review course. These are pricey but many of the premed students take them because getting a decent MCAT score is absolutely vital. Taking the review would help you spot where your weak points are. Then you could study up, and take it again in a year or two.

It is not necessarily a bad thing that you have been out of school. The med schools seem to like the idea of some time off after college to mature. But you will have to totally convince them that you can handle the firehose system of learning that occurs in the first two years of med school.

There is a lot of info about med school appls on the website of the American Association of Medical Colleges AAMC.

Good luck.