Flagging can be helpful – it is possible that, despite being completely lost on a particular topic, you may see something later in that testlet* that gives you a lightbulb moment regarding that question.
* I can guarantee with near-certainty that you will see a question in #2/#3 that basically spells out the answer to a question in #1, but of course by that point it's of no use!
I will second what Kimboroni said (and I like his/her method) about time management. You could develop a system like this (in conjunction with other test-taking strats like first eliminating non-answers, etc.):
1) If you know the answer, select it and move on.
2) If you're not sure but have a good guess/instinct, select the answer and flag.
2a) If you're not sure at all then leave it blank.
This way, after you finish #24/30 you can go back to the beginning and review like this:
3) If it was flagged then just reread the question to make sure you haven't glossed over a critical element. If something sticks out, reevaluate; otherwise your first instinct is probably correct.
3a) If it was left blank and you still have no clue either go with C or whatever you feel is the best of the rest.
Be careful in your review, however, as a LOT of time may potentially be wasted on step 3. Most people will probably tell you that they wasted time talking themselves out of the correct answer as opposed to changing for the better, but I believe that a second look doesn't hurt provided you ADHERE TO YOUR TIME BUDGET.
FWIW I used every second of the allowed time for AUD, REG, and FAR, and although I would have liked more time to review my SIMS I wouldn't say I felt overly rushed during any of them. I finished BEC an hour early because I had a lot of theory (as opposed to calculation) MCQ's and, quite frankly, 3 WC's are child's play compared to twice as many SIMS.
B 92
A 99
R 90
F 92
Becker Self-Study
OH CPA since 2/18/14