Hopefully you have a good and dedicated high school guidance teacher. They will need to help you choose to right major, classes, give recommendations and basically chart your course.
Choose your classes including electives. Some classes require you to take certain classes before you can take the class you want so make sure to research all of your desired classes.
Don't take easy classes. Admission Officers would rather see you do OK in really hard classes then get an A in a bogus class. Make your schedule challenging but still in reach.
To stand out your going to need extracurricular activities at your school and in your community. Its good to have a few but don't kill yourself. Make the ones your in be very moving to an Admission Officer.
Visit and become acquainted with many of the faculty and find out and special things that may help you or get a friend in high places.
APPLY. Your going to have to fill out your FAFSA at fafsa.ed.gov
They will automatically tell you if you apply for any grants or scholarships. You may need to research into additional private scholarships; there are a TON of them out there. Do all those little 500 ones they add up very quickly. Most schools offer programs to work for the school in return for free or reduced education if you are interested.
Your going to need your transcripts, college admission test scores, and visit with an admissions officer before you find out if you get in.
Pray.
Good luck!