1. Get your GED If you didn't complete high school, make sure you get your GED. It's hard to find a job with no additional training, but even harder to find one without at least having graduated from high school. Some career centers won't even accept you for their programs unless you're a high school graduate or you have your GED. If you don't have it, your local career center likely offers GED courses.
2. Speak English well...and learn another language if you can Another basic rule for most any job is that you need to speak English. If you speak good English and a foreign language, you'll actually be more likely to be hired for a job. A lot of employers like to hire people who speak two languages. But if you want a good job, you have to have good English. If this is a problem for you, your local career center also probably offers classes to help you improve your English. If you speak another language and are just rusty with it, or have people willing to teach you, learning a language (particularly one like Spanish) never hurt anyone looking for a job.
3. Get more training. Being trained means you're not fighting over the same job with everyone who's ever graduated high school. You're just going against people who have training in the same field you do, which is a lot fewer. Read more about job training at Good Jobs, A Little Training.
4. Stay in school! Every year that you're in high school is a year that you don't have to make up in a GED class. Plus, many high schools offer job training. Medical academies are pretty common in high schools, where you can get certified to be a home health aide, first responder, or EEG aide. The great thing about that is when you take the classes for certification in high school, you're trained for a job after you finish and you didn't have to pay anything for the job training. Check out the academies that offer job training in Polk high schools here.