Any advice for avoiding careless errors?

Yes! Slow down.

I say slow down, when what I really mean is relax. The difference, measured in seconds, between the amount of time it takes you to read a sentence:

"As to the issue of Justin Bieber's romantic inclinations, I could care less"

or to correctly read the sentence:

"As to the issue of Justin Bieber's romantic inclinations, I couldn't care less"

almost can't be measured.

Probably you can't measure it using your wristwatch, anyway. But that miniscule difference in time means the difference between an author caring about the Biebs' love life in the first instance, and not caring about the Biebs in the second.

To catch that distance, you just have to read, which shouldn't be hard, but sometimes is hard nonetheless. So my best advice to you is to try to slow down, just a bit. You have the time to read properly. Make yourself know that - where it counts - and your actions will start to reflect it.


Another thing that may help you bring it home:
Think about the math. How many careless errors do you make in a section? We'll fictionally call it two for now.
If you slowed down enough to not make those two careless errors, even if it meant going so slow that you didn't have time to answer the last question, you'd still be better off! (Because you'd pick up two points for the four-fifths of a point you gave away by guessing on the last question).
And this effect is amplified if you skip very difficult questions as you encounter them: If you go methodically enough to avoid your two careless errors, and then run out of time and don't get to answer the incredibly-difficult question 18, you've gained two points, and probably haven't lost anything at all - question 18 was so hard there's a good chance you would have missed that one even if you'd worked on it.
And if you can internalize these facts, this should help you slow down enough to stop making careless mistakes.

I think that will help. Hope it does.