It just makes you not care that you've done a bad job.

I had a friend who has this pretty bad. Her freshman year of university, she would smoke mainly on the weekends and whatnot so she wasn't a stoner by any means, but when she moved out of the dorms, she was smoking almost daily. Her grades started to fall at that point, but then she quit for a small amount of time and her grades went up. She went from first semester organic chemistry where she would get 20 points below the average every time to getting 5 points above average on the first exam of the second semester. Then she went back to smoking weed all the time and her grades went straight back down. Her response was to get really high and try to push it away. The last day I saw her, she straight up said "I can't find motivation to do schoolwork at all anymore". She even went on to say that it was really bad how she just didn't feel productive.

Mainly what I'm saying is if/when you get a bad score, don't dull that emotion out with alcohol, weed and so on. Actually use that anxiety to do work. (I'm not saying to not have fun, just to be responsible)

Also, other tips:

Ditch your phone. It's really tempting to procrastinate on that shit.

Take breaks unless you have some crazy motivation and focus.

Find a someone in each class to study with: probably a friend, someone from your dorm, someone from discussion/lecture, etc. because it really helps to find someone that you can help or someone that can also help you. OR just find someone to go to the library with on a regular basis.

Last, the type of class permitting, notecards. Make those fuckers.