What are efficient ways of studying?

So, basically, I’ve been slacking off this year, and I haven’t been applying myself to study. Part of it was pure laziness and the other part was because of health issues. I’m tired of under achieving and now I actually want to try for the last marking period, but I have one problem: I don’t know how to study. I’ve never studied before, I usually relied on memorizing the material in class, and then studying for a half hour to one hour before the test. However, since my classes are getting harder, I want to get my act together. Does any one have ideas on the best way to retain the most amount of information?

The most important thing is to make sure you understand the information. If you don’t understand it, just reviewing and memorizing won’t help. Ask teachers, parents, other students/friends to explain if you don’t understand.
Then you need to interact with the information as much as possible, so look at resources other than the ones from school. If you can find a way to connect it to other things you understand, it sticks better.
Reviewing the information with other people in your class is good too. For example quiz each other on the test topic and have the person explain the topic if they don’t get the answer right. Explaining concepts to each other or people who don’t know anything about the subject is a good way to make sure you understand the topic.
Practice problems over and over, especially ones you keep getting wrong.

Passive studying (just reading the information over and over again) doesn’t help with retaining a lot of information. Do active studying such as making charts/organizers, flashcards, quizzes, explaining information…
Having a study group/partner is also often more effective than studying on your own, but that depends on your learning type and if you actually study when you’re in the group or get off topic and waste time.