I have 16 ASE certs and have been a master tech for 25+ years, if you have a general idea of the systems buy the books or check with the local library and read them. With some common sense and eliminating some of the answers they give you to pick form its not that hard. Its a multiple guess test and if you can eliminate 2 of the answers you have a 50/50 shot. Relax and read a pretest manual for whatever you want to take.