Timing and Comprehension: after you have selected your exam, diagnosed, and trained, it's time to work on speed. Being able to answer exam questions is important, but it's NOT enough. You must be able to answer questions UNDER TIMED conditions--and that adds another, very substantial level of difficulty. You should ONLY use real officially released exams to test your timing and comprehension. Once again, no test prep company can exactly duplicate exam questions. So it's critical to use official questions to test your speed. If you used one of the SAT's and one of the ACT's to verify which exam appeals to you and then you used your answers from that same test to diagnose your strengths and weaknesses, that means you will have three (3) full length exams remaining for your use.
When testing your timing, you don't need to take a full test. You can use a single section at a time to test yourself on that area. Example: if you have just finished prepping for math, take a 45min or 60 min math section, set your timer and take just that subsection under real timed conditions. Don't cheat or fudge--you'll only hurt yourself. Then score your results and see where you still need work.
Following this method, the three (3) remaining exams will provide sufficient opportunities for you to test yourself repeatedly. Towards the end of your prepping you could also test yourself again with a full length exam.
Continue the process of test, diagnose, train/prep, test timing, diagnose results..then back to training/prepping and so forth.