Create a weekly schedule [below] for yourself. Start by scheduling fixed blocks of time, such as class or work time.
Then, block out two hours for every hour you spend in class. For example, if you are taking 12 credits, plan 24 study hours into your weekly schedule.
Be sure to set realistic goals for yourself by including some time for errands and for having fun. You may want to plan some "flex time" into your schedule for unexpected things that might come up throughout the week.
It is also a good idea to have a calendar so you can keep track of important deadlines, assignments, exams, group meetings, and campus activities.