Be specific regarding the task that you hope to accomplish during each planned study period.
Use daylight hours
Research shows that 60 minutes of study during the day is the equivalent of 90 minutes of study at night.
Study Soon After Lecture
Retention and understanding are aided by a review of your lecture notes immediately after class: eg., one study showed that students who wrote a 5-minute review test following a lecture remembered one and a half times as much material as students who did not review, when tested 6 weeks later.
Do tasks according to priorities
Remember Parkinsons' law that "work expands to fill the time available for its completion." If you allot 2 hours to read 10 pages, it'll probably take you 2 hours to complete this 30 min. task.
Start ahead of time
Avoids cramming and the resultant poor quality ("If only I had more time...")
Discover how long to study
As a rough starting guide, for AP classes, every hour in class you should plan to study for one hour outside of class. Then, adjust up or down as necessary to achieve your goals.
Plan blocks of time
In general, optimum efficiency is reached by planning to study in blocks of one hour -- 50 min of study followed by a 10-min break. Shorter periods are fine for studying notes and memorizing materials. Longer periods are often needed for problem solving tasks and for writing papers.