I would take a look at your subset scores and see where you struggled the most. Focus on that section (and the others your struggled on). ASVAB is similar to any other standardized tests:
1. Learn the mechanics of the test and understand HOW to take the test
2. There are a lot of free ASVAB test prep resources. Research them and dig in on the test prep
3. Repetition/practice is the key to increasing your scores - work the problem sets over and over and over.........