Don't multitask. Concentration is incredibly important for retaining your memory.You need to keep things simple. This is why you enter a room and forget why you came in. It's because you were probably planning your party at the same time, or thinking about the TV episode that you just watched and you weren't concentrating.
When you're studying and trying to remember things for school, then focus on that one task.Don't think about that friend's party from the weekend. Don't try to do a bunch of different tasks at the same time, or you won't get the full benefit from any of them.