Before you apply to colleges, in your junior year of high school, take some time to think about your current academic achievements and ask yourself some questions: Are you in the top 10 percent of your class? Are you set on becoming valedictorian? Have you already taken the SAT or ACT several times? Do you want to graduate college in 3 years? Do you already know what medical or law school you want to attend? If you said yes to any of these, you are highly motivated and well on your way to fine-tuning the goals you already have in place.
But also--if your grades are excellent in high school, is it because you really put effort into studying, or is it because the classes are not challenging enough for you, and therefore you need not do any work to obtain excellent grades?
On the other hand, if you don't care at all about grades, college or a career, you need to get serious fast. Maybe you can get away with apathy toward your grades in high school, but you can't do so in college without major consequences, like being suspended or kicked out college--something that will stay on your record.
College will definitely be more of a challenge, for many reasons, than high school, regardless of what situation you find yourself in currently.
Realize that you will have to be flexible. As discussed by Robert H. Miller in his book "Campus Confidential," your ultimate goal in college is to "try and find your passion" so you can contentedly and successfully continue into academia or the workplace after graduation. That said, you will probably change your mind about your major once or maybe several times. As you take classes in new and different subjects, as you meet other students and talk with your professors, your mind will be opened up to a slew of possibilities that you had never considered. Just be sure to let your mind stay open, and give fair consideration to a whole new career path, even if your parents had their heart set on you doing something completely different. It's not up to anyone but you to decide what you are going to do with your life.
Don't forget that, in most cases, you will no longer be living with your parents, so it's up to you to, in addition to making time to study, do your own laundry, make your own dinner and do your own dishes. You will certainly be independent, but with that independence also comes great responsibility. You make your own choices, without any parents nagging you to do your homework this time, and you pay for your own choices. This must be taken into consideration as you set your goals--your ability to balance responsibility with the freedom that college allows.
According to a report on goal-setting by Ithaca University, "The best goals are specific and measurable." Be sure to divide your larger goals into small, feasible steps over a specific timeline. Don't set vague goals, or the steps to reach that goal will be impossible to define. If you want all As for a semester, you must ensure that you attend every course lecture, study hard for each exam, and maybe speak with your professors to let them in on your goals so they can also help you. But more concretely, you must write out a detailed schedule of the amount of study time each day that you will allot to each course.
Also, the more people aware of your goals the better, since they can support you, give you constant feedback and a give you a reality check as well. And be sure to reward yourself each time you get a little closer to your goal.