1) Don't Multitask
Contrary to what you believe, multitasking actually diminishes your performance in all the activities that you're simultaneously doing. Several studies have shown that the human brain simply does not multitask very well. You can read more details about one particular study here. Just as studies have shown that driving while talking on the cellphone is dangerous, studying while watching TV and Instant Messaging and listening to music can be dangerous for your grades.
- Turn your cellphone to vibrate, even better, turn it completely off so you're not tempted to check it for messages.
- Don't have a movie or TV show running in the background. Humans are very visual creatures, and having multiple visual stimuli only lessens your focus
- If needed, use earplugs. They're the cheapest way to build a "quiet zone" and prevent sensory overload from distracting you
2) Don't Hesitate to Ask
In this modern age of cellphones, texting, instant messaging, and emailing, there is no excuse for not asking questions when you're stumped. Instead of surfing Facebook while pretending to "think" about a seemingly impossible hard problem, you should be asking your friends for help. Chances are one of them will know the answer, and you can be on your merry way. It's a win-win-win. You've made your friend feel important and wanted by asking for help. You've gained knowledge in a mere seconds. And you didn't have to lose your focus because of some really hard problem.
3) Don't Just Read
This may be the biggest trap students fall in to. You get your test back and it's not the score you wanted. "But I studied for so long," you think to yourself. Simply reading your notes or textbook isn't studying. Watching a Nascar driver manuever turns doesn't qualify you for the next big race. You have to get behind the wheel and actually do some driving yourself. It's the same when it comes to studying. In addition to reading, you have to "do work". This could mean summarizing chapters by typing up notes. Or working through practice math problems. Or discussing concepts with your friends. Here's a simple litmus test: until you're comfortable explaining an idea to someone else, you yourself haven't really understood it yet.