Read up on health, earth science, chemistry and biology to score well on the ASVAB. The general science portion of the exam uses questions about each of these four subcategories.
Take general science practice tests online to test your basic knowledge. Practice tests for each of the subcategories are available on the ASVAB Score Headquarters website (asvabscorehq.com). Once you submit the practice tests, your grade and the correct answers to all problems are given to you; this provides you with an idea of the subjects you need to study prior to taking the ASVAB.
Review your practice test scores and focus on the areas in which you have trouble. For example, you could have no trouble on the biology portion of the practice test, but you might struggle with the chemistry section, which means you should focus your studying primarily on the basics of chemistry.