ASVAB is not a "test", but nine concurrent tests. It consists of nine different subjects with different periods for each subject. This is not a test of intelligence, as some people think, and it is not about a specific topic.
It tests your general knowledge in various subjects and indicates your ability to work under pressure. This shows the military how well-suited and "trained" you are for certain occupations and you can learn it from the greatest ASVAB study guide.
If your goal is to become an expert on all topics covered by ASVAB, you need to work upon it. ASVAB has nine different subtests. What you might not know is that four of these tests determine your registration qualifications. This is known as the Armed Forces Qualification Test. The other five sub-tests determine the work that you can do after registration.
If your main concern is general inclusion, you need to focus on the four subjects that make up AFQT: Arithmetic Thinking (AR), Paragraph Understanding (PC), Word Knowledge (WK), and Mathematical Knowledge (MK). You now have four areas to cover rather than nine, and your day becomes a little brighter.
If you have a particular job in the military, you should check the line assessment requirements for the position and focus on issues in addition to ASVAB AFQT related to the job. The best way to learn ASVAB is to do as many ASVAB pre-tests as possible. You might want to look for free ASVAB tests online.