Great question which will get a lot of opinions. Here's mine.
First, do well in school! Stay out of trouble. Bad grades and off field issues are tough to overcome.
Film. As mentioned good film is critical. Most high schools hire a student to sit on the roof of the announcers booth and shoot enough video to be able to use for the teams film review, but they tend to shoot terrible video. They might have a Hudl account. Garbage in, garbage out. If your team doesn't shoot good film you either need to shoot it yourself or hire someone to do it. There is plenty of free software for making a highlight video. Try CNET.COM for free software. Make your tape no more than 4-5 minutes. Don't include marginal plays to extend the video. Parents tend to look through rose colored glasses and make tapes too long. Don't use crazy effects, slow motion repeats of plays, long intro's, nasty rap music, etc. Look at how Scout and Rivals format their tapes.
Important: Pick the 4-5 absolute best plays and start with them. Many coaches will move on if they aren't impressed by the first couple of plays. Get your coaches to help select the plays. What might look good to you might show terrible form or some other detrimental feature to a coach.
Publish the film on YouTube and send links in every communication you make.
Resume: Put together a one page resume with all your contact info, parents names, e-mail addresses and phone numbers, stats, GPA, test scores, awards, etc. Generate a .PDF and include with all communications.
Recruit forms: Most colleges have a potential recruit form. Take the time to go to the websites of any colleges you are interested and complete their forms. That gets you into their systems. Most will have a spot for your YouTube or Hudl video link.
E-mail letters to coaches, area/position scouts and recruit coordinators expressing your desire to play for their school. Always attach your resume and include links to your video.
Register and get profiles on Scout.com, Rivals.com, 24/7, etc.
Camps and combines: Look at doing SPARQ testing. Try to get invited to the Nike Football Training Camps (NFTC's). Attend camps at your top colleges. Possibly attend skills camps in your area. Get exposure.
Visit colleges, meet coaches and establish relationships.
If things don't seem to be happening you might want to get a professional evaluation as to your true skill. Aiming for a D1 career when you are truly a D2/D3 player means you might be ignoring the schools you should be talking to.
If all else fails you might pony up the money and put yourself in the hands of a recruiting agency like NCSA. Remember that their job is to get you into a school, but it might not be where you were hoping to go. There are tons of schools in the midwest and northeast looking for players. Most of the players are in the south and west. NCSA hooks them up. FYI their prices are negotiable.
Work hard, be persistant.
Good Luck!