Here is a famous letter, presumed to be from St. Thomas Aquinas, on how to study well. I have yet to put some of this advice to practice...
Because you have asked me, my brother John, most dear to me in Christ, how to set about acquiring the treasure of knowledge, this is the advice I pass on to you:
That you should choose to enter by the small rivers, and not go right away into the sea, because you should move from easy things to difficult things.
Such is therefore my advice on your way of life:
1. I suggest you be slow to speak, and slow to go to the room where people chat.
2. Embrace purity of conscience; do not stop making time for prayer.
3. Love to be in your room frequently, if you wish to be led to the wine cellar.*
4. Show yourself to be likable to all, or at least try; but do not show yourself as too familiar with anyone; because too much familiarity breeds contempt, and will slow you in your studies; and do not get involved in any way in the deeds and words of worldly people.
5. Above all, avoid idle conversation; do not forget to follow the steps of holy and approved men.
6. Never mind who says what, but commit to memory what is said that is true.
7. Work to understand what you read, and make yourself sure of doubtful points.
8. Put whatever you can into the cupboard of your mind as if you were trying to fill a cup.
9. "Seek not the things that a higher than you."
Follow the steps of blessed Dominic, who produced useful and marvelous shoots, flowers and fruits in the vineyard of the Lord of Hosts for as long as life was his companion.
If you follow these things, you will attain to whatever you desire. Farewell.
*This reference to the "wine cellar" is actually a reference to Bernard's commentary on the Canticle of Canticles, and signifies the place of wisdom.