It's one of the hardest life-skills for many of us to master: time-budgeting. In an ideal world, we would all go through the following train of thought:
1. To improve at anything, we need routine.
2. Routines take place in the same location, at consistent times. To establish a routine, we need to make time for ourselves.
3. To make time, we have to budget time.
Sounds simple, right? But this is a skill that escapes most of us because, as psychiatrist M. Scott Peck so famously noted decades ago, human beings are basically lazy. This is the fundamental sin of our species. We are, at bottom, unwilling to work to change ourselves, because it's so much easier just to remain where we are-- content, complacent, and unfulfilled. What's the remedy?
To be honest, I don't think there's any easy way around this problem. Laziness is a form of entropy, a downward-pushing, disorderly force that makes us resistant to the ordering processes of progress, evolution, and self-improvement. At the most basic level, there obviously needs to be a desire to improve yourself, but desire without direction leads nowhere.
It might help if you began your self-improvement with a clear vision of what you're trying to accomplish. For example, if your goal is to get into a non-Ivy League college, then it makes little sense to tell yourself that you need to score a perfect 2400 on the SAT I. You don't. In fact, many Ivy Leaguers didn't make perfect scores, either: they were admitted thanks to decent SAT scores plus other academic (and non-academic) merits-- their consistently good grades, their community-service extracurriculars, their student leadership, etc. Their SAT scores weren't bad, to be sure, but they didn't need to be perfect. Opposite case: what if your goal is to be an engineer (mechanical, electrical, civil, etc.)? In that case, I strongly recommend that you shoot for an 800 on the Math portion of the SAT I, because without that perfect score, you reduce your own competitiveness. If you're trying to get into Georgia Tech or Virginia Tech or MIT, you're not helping yourself by showing those schools' admissions committees a score of 700; many of the other applicants will have scored 800, and the schools want those applicants.
The upshot of all the above? Scale your goals to meet your ambitions. Figure out what your ambitions are, then strive for them, but do so realistically. Make a plan of attack. See where you are, grade-wise, in all your classes; figure out where you want to be in those classes; create a study schedule that will give you space to establish a routine. Cut out anything unnecessary to the achievement of your goals, and be wise with your free time. Be sure to include free time for yourself, but not too much. Now is not the time to be lazing around.
2. Specifically on Test Prep
Everything I've just written applies to how you should approach your test prep. Set realistic goals for yourself: "A 2400 would be nice, but for my purposes, I need to score at least a 2000, with Critical Reading being at least 700. That would get me where I want to go." Drill yourself by going to a test prep center (that's a good way of having a routine established for you), or take the cheaper route: buy the College Board's official guide to the SAT I, take the diagnostic test to figure out your weak points, then develop a plan of attack based on what you discover.
Achievement requires sacrifice. If you're not satisfied with your diagnostic score-- if, for example, you scored a 1500 overall-- then be sure to ratchet the level of your commitment upward so that you meet your goals. Be ready to turn aside opportunities to go see movies with friends, or to watch as much TV as you used to, or to surf the Net or text or tweet or use Facebook until all hours. Attack your goals with seriousness of mind. Remind yourself, again and again, of why you're going through all this trouble. The reward will be worth it.
Routines require stability. Your study should take place in the same location, at the same time of day, with a minimum of distractions. Stay away from TV, younger siblings, friends (unless they're actually studying with you!), and your smart phone. When studying the Math portion of the SAT, try to avoid calculators, even though calculators may be allowed. Don't vary your study time-- 6PM on Monday, 8PM on Tuesday, 7:30PM on Wednesday, etc. This is more harmful than helpful.
There's also nothing wrong with involving your parents or other adults in the study process, as long as they can offer competent help. Many parents will readily admit that they can't help you, and you should probably take them at their word. Seek help from a trusted neighbor, fellow church/temple member, or parents of a classmate. Ask these people to quiz you on your weak points.
In conclusion: there are no magic solutions. Time-budgeting is a matter of knowing where you want to go, taking those goals seriously, and establishing a routine that will get you there. Any strategy you adopt will require a certain level of desire, focus, self-discipline, and all the rest. If laziness is a form of entropy, then self-improvement means fighting against that natural tendency to be idle and complacent. Unfortunately, many adults take this lazy path, then spend their lives wondering why they didn't pursue their cherished desires when they were younger. Don't be one of those people. Make time, keep your goals in mind, and push yourself to achieve. When it comes to test prep, find your weak areas, establish your routine, and set about shoring those areas up. You can go it alone (in a distraction-free environment), or enlist the aid of friends, parents, or other trusted adult resources. Private tutoring (such as what I offer) or tutoring centers are also an option, if you feel you're not self-disciplined enough to fix your own schedule. Whatever you choose to do, keep at it!