Things to consider:
1) Study with good friends who work hard OR study aloneTry both out and see which option produces better results. Your one and only measure of effectiveness should be the quality of your study at the end of the day.
Sometimes I study with friends because we help reinforce one another's knowledge. I find that very effective for some subjects. We spend abt 25% of the time on study breaks and having meals and 75% of the time with our faces buried in our notes or discussing our coursework. We study from morning 9am to about about 11pm at night.
Sometimes I study myself because that day I simply feel I need to be alone to concentrate. Normally the subject im working on that day requires alot of memory work.
2) Study location. Where to go? Preferably not noisy places like macdonalds or possibly faraway places like the Changi airport. Find somewhere nearby that is quiet and peaceful. In school or in the vicinity of school or home. I alternate between school library and the voiddeck near my home.
Close to exam period, my library will be totally packed with students studying for exams and this gives me motivation to study as well. It also reminds me that i am not alone during those difficult times.

When i study at the voiddeck it is because im too lazy to travel to school or i want to study alone that day.
3) Study timingWhether more effective during the day or in the evening. Find out when you are most effective and allocate the time slot to subjects that require most attention.
4) Study PlanNo two ways about it. All things being equal, people who lay down a study plan do better than those who do not. A study plan allows you to have a sense of purpose when you wake up in the morning. No more uncertainty about how you are going to spend the day.
Right away you know what you need to study each day. No time wasted thinking about what you WANT to study because you know what you NEED to study already.