Study in chunked sessions: Your ability to retain information diminishes after about 25-30 minutes, so break it up into multiple, smaller sessions. Reward yourself with fun activities during your breaks
Have a dedicated study area: Don't study where you do anything else. Don't study in your bed, where you play games (even if it's your computer), or in front of the TV.
Know the difference between recognition and recollection: Recognition requires a trigger for you to remember something and you may not get that on a test. Study actively with focus on recollection. Quiz yourself and don't just glance over highlighted notes.
Take good notes: Find a note-taking method that works for you and expand on them after your class lecture to increase retention and understanding.
Be ready to teach what you've learned: If you can teach it to someone else, you have a solid grasp on the material.
Read textbooks effectively: Use the SQ3R Method—survey, question, read, recite, review—to actively retain information. Just reading it is not enough.