There are a variety of Education courses(P076, P077, P101, P102) designed specifically to teach students how to study. Since many of the counselors teach these courses, you can also make an appointment to see a counselor regarding study tips.
Although this will depend on the class, it is generally recommended that you study 2 hours per week for each hour of class. So if you are taking a 3-unit course (that meets 3 hours a week) you should plan to study 6 hours during the week for that class.
If you feel that you may have a learning disability, stop by the Disability Resource Center in AC-115 to make an appointment to see the learning disabilities specialist. There are a variety of diagnostic instruments that can be used to determine if you have a learning disability or not.