The Tif'eres Yisra'el (Bo'az, Avos 1:15) gives five points for success in learning and improving the memory:
Not to learn lazily (lying down, leaning, or eating when learning), and not to concentrate on things other than learning. A person should learn out loud to fix this. The gemara tells a story of someone who learned quietly and forgot all his learning after three years. A person shouldn't concern himself with his worries while learning. He shouldn't be extremely happy or sad, excluding the joy he feels because of the learning.
A person should be calm while learning. There should be no distractions in the room in which he is learning. The room should be spacy and have windows. The book from which he is learning should have a clear print.
A person shouldn't take breaks in the middle of learning one thing. A person also shouldn't switch from learning one thing to another so quickly; he should learn a maximum of three things a day. A person shouldn't switch from edition to edition of the same book, from room to room, or from spot to spot in the same room.
Understand the subject well. Once you understand it well, be able to memorize the main idea without looking in the book. A person who wants to make a speech in public should review it a few times the night before and a few times the morning of the speech.
Be in a place where there are no distractions. If you encounter a distraction, strengthen yourself to not pay attention to it.
In his commentary to Avos 2:14 (Yachin 129-131), he writes that a person needs three things for success in learning:
Review everything you learned the next day.
Be able to answer these questions: Who? What? To whom? When? Where? How? Why? Look in the thing you're learning and ask questions such as "Why did it have to use this extra word?" and try to answer them.
Concentrate solely on your learning and don't pay attention to any of your worries.
Also, in Avos 1:13, we learn that one who doesn't increase his learning will forget.