You should take naps often. This may be very easy for some.
For others, you may have to find some time to take naps. College/University will definitely keep you busy and it may be hard to find some time to rest.
At least 30 minutes of napping is sufficient; just don't go over an hour and a half. Napping helps you to recharge and it also helps you to retain the information of what you recently learned in your mind.
There are many places where you can nap: libraries, desks, benches, your own room, and anywhere else that is quiet and safe enough to keep your belongings secure.
Just try not to nap during class!