Go to your congressman and senators' websites. Go to the link for Constituant Services and they should have the procedures listed for applying for a nomination.

My son had to fill out applications, submit SAT and ACT scores, and I believe his grades, a resume, and an essay. They sent him a letter with information on an interview.
get a good start on everything. get everything done as early as you can!
get a good start on everything. get everything done as early as you can!

Our Congressman had a deadline of 10/14/2008, 1 Senator had the same date, and the other Senator's deadline was 12/31/08.. Make sure you check each one!!

Either before the end of the school year or AT the beginning of the School year you should have some of your teachers preped or already have letters of recommendation from them. The MOC requested letters from not just teachers, but counselor or principal AND someone in the community.

For the nomination packets my daughter had letters from:

Her counselor (also her basketball coach)
Her principal
Her Girl Scout leader (also a family friend)
Her Church Youth Group Director (he is in charge of their annual missions)
Her Pre-Calculus Teacher (he has been her teacher on and off since 8th grade)

The Congressman wanted a 2 page resume, the Senators did not. You will also need to ensure that your SAT/ACT scores are either sent to them after you test OR get them official transcripts from school that will have those scores. Be attentive to dates of the tests you take and their deadlines for nomination requests.

My DS had an interview with the Congressman, but not the senators.