Hey, I'm entering my third year in college and I have some advice!
1) Your planners are a great guide to figuring out when to get things done. You can always rearrange things as you see fit (which is why I use the word guide), and try to leave some time for you to relax every day. If you plan things in advance, you can allot maybe an hour of your day every day, or every other day, to finish that big project that's due in a week, instead of worrying about it last minute.
2) If you have any assigned readings, and a lot of spare time (like at the beginning of the semester) it helps to read ahead so you're not as swamped later on.
3) Youtube videos and online resources are free and a great way of tutoring yourself if you need a little extra help. Highly recommend crashcourse on youtube and khanacademy.org.
4) Don't be afraid to ask your teachers or counselor for extra help! Teachers will help you figure out what you're not understanding and fill in that missing link. I say counselor because I had a lot of trouble keeping up with work due to personal circumstances and she was able to talk to my teachers and have them ease up on deadlines for a while. If you talk to some teachers in advance, they'll even give you an extension
5) If you can, get a spare period. Just some time so you can either hang out with friends, go out, or catch up on some work if you really need it. This isn't possible for everyone but it's a nice option to have.
6) Ask your peers for help! Other students can help keep you in the loop, or help you deepen your understanding of subject content through group studies. Having a friend look over your work is great too.
7) Take advantage of your schools studying areas. If I knew I wouldn't want to study after school, I'd quickly eat my lunch and hit the quiet study area and just go over whatever content came up in the last few classes. Then I'd be free as a bird later on.
8) And, something that I needed to hear: It's okay to make mistakes. You're still learning so don't get mad at yourself for not understanding something right away. Things take time : )
College is a bit more annoying because depending on what school you go to there's little to no guidance on what you need to do in terms of confirming your spot/paying/getting your scholarships and bursaries. Literally had to be on my college's case 24/7 to get the money they owed me LOL. But my advice for college remains the same with the few other points:
1) Your readings are usually a lot longer than they were in high school (depending on your program), so break them up so you don't bore yourself doing them all in the same day. Do them sometime before the corresponding lecture though.
2) You're paying for your classes so go to them! Exceptions are classes where the profs are just reading off of powerpoints they have posted online/from the textbook. I can guarantee you can go through that content in like half the time.
3) Don't purchase your textbooks right away (if you're going to buy them). Sometimes profs don't use the book bc they're cool and they give you all the notes you need for the semester, or sometimes they use a newer edition that just came out. Usually older editions will get you by though.
4) When taking notes, I usually add comments/notes to whatever powerpoint the prof has posted to avoid spending years on going through a single chapter.
5) Join your program's/year's facebook page to keep note of deadlines and see if any older students are selling their books. Good place to discuss/ask questions c: