learning from mistakes

Also, keep a list of problem you do - in a notebook, in an Excel file, whatever.

Every time you make a mistake, make a note of exactly why you made the mistake (didn't know the content? forgot something? calculated incorrectly? made a careless mistake? read the question wrong? and on and on).

Once you know why you made a mistake, you can come up with a plan for what practices / habits to implement to minimize the chances that you'll make that same kind of mistake in future. But you can't do that until you know what's causing your mistakes!

There are almost always multiple rules being tested in a single sentence, so know that from the start. Deal with the original sentence first - if you can find any errors there, cross off A and also cross off any choices that repeat the exact same error.

Once you've exhausted any errors you spot in the original sentence, compare the remaining choices, but compare them VERTICALLY - that is, look for differences in the same parts of each answer choice. The differences tell you what the potential errors might be (though sometimes a difference doesn't actually indicate an error). Start with whatever differences you know are errors and, specifically, start with whichever difference you feel most confident about. Keep doing this till you have only one choice left.

For the subj-verb errors, as I mentioned before, figure out WHY you're making the mistakes you make. Then you can actually figure out how to combat those mistakes.

Excellent - that sounds like a good plan for SC!