Step1
Check your attention span. Attention span is the time limit of the mind's ability to focus and concentrate on one task. The average attention span of a 13-year-old 35 years ago was 15 minutes. Today, the attention span of an average adult is 20. These adults are the product of a society that aims all of its media programming at the old 13-year-old standard. You can develop your attention span by turning off the TV and computer and spending a little more time each day on a given task. Start with things you like to do--reading fiction, building models--anything that requires you to be an active participant. After you're able to read or work for an hour or more at a time, switch to something less enjoyable like reading non-fiction or assembling a bicycle for a neighbor's child. When you can spend an hour or more doing a task you don't particularly care for, you've expanded your attention span beyond that of the average adult!
Step2
Check your "Input" Skills. Listening, Reading and Note-Taking are all skills you'll need in college and in life. There's usually a lot of emphasis placed on reading in schools but not so much on listening. And it seems that every teacher you have expects that the teacher you had last year taught you how to take notes. College tests all three. You will have tons of reading, sit in large groups listening to a professor hold forth on a subject. None of it will be in your textbook--if the course has one. Your notebook will be your only friend the night before the final. Learn to listen to instructions and take notes!
Step3
Check your "Output" skills. Writing, speaking, presentation and participation determine the way the world sees you. Whether you are applying to a college or going straight to a job interview, anyone who is going to invest their time or money in you wants to know whether you're up to the task and what you bring to the table. If you can't write a coherent paragraph, express your ideas clearly in written and spoken language or ask worthwhile questions, you're behind the pack.
Step4
Check your technology skills. Computer skills have become as necessary as readin', writin' and 'rithmatic. You only know how to play video games and blog? Grow up. The 'net is used by the whole world, not just adolescent gamesters and groupies.
Step5
Make a List of Strengths and Weaknesses. What sorts of things are you able to do easily? What successes and failures have you had? What keeps you from being successful in classes (beside not getting enough sleep, too much sugar and too many activities)? Sort your list of weaknesses into things you can fix with courses and things you'll need help from parents or counselors to address.
Step6
Find courses that help you address the weaknesses you've identified. If you need help listening and taking notes, take courses where lectures are given and most of what happens in class is oral (like classes in history and the social sciences). An English teacher can (and should) give you help with note-taking. Consider courses that require research projects and in which students report to the class on their projects. These will aid in developing reading, writing and presentation skills. Speech courses are, unfortunately, almost a thing of the past but a lot of English teachers take a stab at getting you to organize what you need to say. And don't forget science and math. The logic and analytical thinking that you develop in these courses contributes to problem-solving abilities way beyond geometry and physics problems.
Step7
Do take college-prep courses even if you don't plan on going to college: expect your counselor or the teacher to be able to list the skills that they will help you develop. Most AP and college prep courses concentrate on literacy skills that will make you attractive to an employer--not just to a college.
Step8
Expand your horizons. Volunteer for some community service. You'll feel good about whatever you do to help, get to know some adults and develop your communication skills in the real world. Colleges (and employers) always ask what kind of extra-curricular and community service activities you've been involved in--it tells them a lot about who you are and how well you'll fit in.