The best way to improve your score while you study for the ASVAB exam is to work on building your knowledge base on the topics that cause you the most problems.
You can look for military test study guide and here are some tips for mastering the main parts of AFQT:
Many students had problems with the math portion of the exam because calculators were not used. The best way to improve yourself in this section is to practice simple pen and paper math.
Look for books on basic topics such as percentages, ratios, basic algebra, unit conversions, and of course word problems.
ASVAB dictionary questions are sometimes hit or miss. If you recognize the word, you should be fine, but if you don't, there's no way around it. The best way to prepare your vocabulary is to practice improving your vocabulary.
There are several scientific subjects that you will test and a thorough understanding will not be sufficient. Your goal in science should be to learn a little bit of each topic every day and then use practice test questions as a guide to further your studies.
ASVAB study guides usually give you a good overview of the science, but exams can ask difficult questions. Keep studying science, memorizing relevant words from the dictionary, and trying to apply them in context.