This advice concerns standardized exams.
These are multiple choice tests, like the SAT, ACT and GRE.
I think Sir Arthur Conan Doyle offered the best suggestion, to wit
When you have eliminated the impossible, whatever remains, however improbable, must be the truth.
It’s easy to game tests of this sort, as the answers to all the questions are contained among the selections! Printed there (or displayed on-screen)—right there in front of you!
So, eliminate the edge cases first. That alone will improve your odds if you have to venture a guess.
In preparation, I think it’s best to just take a lot of practice exams, and focus on the content you got wrong.
You can find print, CD-ROM and online compendiums of these.
My policy was to take them until I scored perfectly 5 times, then go in and do the credit card run (rip-off) to take the actual exam.
You should also practice in the medium you intend to take the actual exam. Many students freeze up if they practiced on paper but are then confronted by questions on a computer display. As McKluhan observed, ‘the medium is (certainly part of) the message.’
I also taught and graded AP calculus and computer science exams for ETS. Students do so poorly on these that any kid who puts anything down will likely get some credit. I remember opening countless blue books containing not even a scratch of an attempt at an answer to the free response sections.
Some wrote extensive summa apologias, begging for sympathy on the part of the grader (usually with a teary lead-in on how hard the latter must be working), or asking for forgiveness for having fallen short of parents’ or teachers’ expectations.
ETS wants to make money. They can’t wash-out everybody, so they’ll give points for partial work.
On the whole, these requirements are farcical, and I hope they go away.
A snapshot score of how a teenager does on a test, with all the social pressures and/or adverse effects of how they felt on a given day is not always a good measure of their promise.
A better measure would be a project, done in several iterations, with leveling up permitted in grading.
The simplest predictor of college success is zip code.