The GRE is one of the most frustrating things about grad school applications. I'd like to consider myself pretty good at math, and I still found it to be insanely difficult. But the previous advice to just practice, practice, practice is probably the best. Take your time to go through it thoroughly, but try not to get burnt out. If you know anyone who's particularly good at h.s. math (i.e. algebra, pre-algebra) I found them to be very beneficial. My sister teaches middle school math and she was always really good at coming up with the right answer and being able to explain it, which the book isn't always clear, so that doesn't help you learn.
Reading the post above, I will add that a lot of schools I applied to really like you to have a combined 300 score, so around 150 for Math and Verbal. Also, many people I've talked to say that schools don't like to see big gaps between your math and verbal, e.g. 140 Q 160 V. (But honestly, unless your sitting in on the Admission committee meetings, who really knows what they're thinking?)
If you still find yourself in a range lower than you would like, I would also suggest schools that don't take GRE scores. I know Central Michigan doesn't look at them. Governors State (in Illinois) may not take them, but coming from Indiana and knowing the schools around here, I had been advised that employers are hesitant to hire people who attended GSU for their Masters. So I would be careful about that.
If you're still in undergrad, or you are still close to some of your professors, ask them about "safety" schools....ones that accept those with lower GPAs or lower GRE, but don't be afraid to apply to some reach schools. You can always explain any discrepancies with your application in your Statement of Purpose/Personal Statement.
Good luck! I'm sure you'll be great!