From someone who has YEARS of experience studying and self-professed "ADD", I can tell you a few things:
-DO NOT STUDY AT HOME!!! There are too many distractions. You will not get any real work done. I prefer the library because it's super quiet and there is no b.s. Just a table, books, and my brain.
-Study in "blocks". Like Quik said, you have to time-manage. Don't try to study for 6 hours straight, you'll burn out. Study for 2 hours, then break to do something physical. Study a couple more, then play some video games. Take 'mini-breaks' if it helps, just like getting a snack or taking a 10 min walk. Exercise will keep your mind fresh.
-Find your own methods. Some people like dead quiet, others like music, others like to study with friends, etc. I personally HAVE to study alone, in quiet, by a window. I take frequent breaks to avoid burnout.
-Depending on what you are studying, making notecards can help, or jotting notes down in your texts. I like to use mnemonics and anagrams...but this is best for tedious science stuff. Repetition is key. Go over all your material at least 2-3 times. Unless you have a photographic memory or are super-interested, once will not be enough.
-If you have trouble focusing, COFFEE!! Not too much though. I also took Ritalin while in college (prescribed), and it helped immensely with concentration. But I'm not advocating this; it can be dangerous and addictive. I stopped after I took my MCAT. I knew a lot of people who took adderall like candy.
There is no magical formula to studying, it is just hard work. Especially if you aren't interested in the material. You should commit to studying 5 days per week, for at least 4 hours per day. That way you get 20 hours a week in and still have 2 days off, as opposed to cramming in one day. You just have to make it a habit.