A lot of questions have subject-verb agreement errors, which can be as simple as whether "is" or "are" is used. To make the error easier to find and the sentence easier to read, find the subject and verb of of the sentence. Cross out unnecessary phrases even, and the sentence will still be readable. For example:
"Ongoing research by several scientists suggest that regular periods of meditation reduce blood pressure and are likely to contribute to other improvements in health."
This sentence has an error in it, but it might be hard to see because of all the extra info. Pared down, the sentence is:
"Research suggest that..." Now we can see that "research", the singular subject, is paired with "suggest", the plural verb. The correct sentence would be "Research suggests..."
Another kind of error common on the SAT is idiom error. It's little phrases like "because of." People just don't say "because to." These kind of things you just have to memorize, and it sucks. I've found this helpful in the past: Idioms and phrases
There's more kinds of errors, but I can't think of any tips for them. Someone else, please?