NCAA Football 10

Simple as it sounds. As soon as you are done with playing through the High School championships, you get to pick your school. Just pick one where you are the starter right away and it should pop up as soon as the dorm room screen comes up.

Quickest way without playing all the High School games is to start a new Road to Glory dynasty using an existing player. Select Buffalo's QB#6 and you should get the achievement within one or two practices. The achievement will unlock once the practice session is over.

As fritzscroll indicated, choosing a school that will offer you a starting position is the quickest way. But if for some reason your choices are more limiting (or you just want to have to work your way up), you will have to earn points in practice to increase your position.

Every time you pull off a "successful" play (the definition of which varies by position), you will earn points. A score at the bottom of the screen will indicate how many points you require to advance to the next level up in the depth chart. You have 10 plays per practice in which to earn points - if you "level up" during a practice session, you don't appear to earn points toward the next level until you start a new practice session. Each practice session will upgrade your player's stats loosely based on his performance during that session, making it easier to earn points as you progress.

Once you earn enough points to reach the starting position in the depth chart, the Achievement will unlock.

Example:
I took a 4th-string HB position. I required 10 points to move up to the third string, 21 points to reach second, and 10 more to reach first (strange scaling - will have to investigate that further to see if it's consistent with other positions).

I would earn points for rushes of 10+ yards (2 pts), catching passes (2pts), breaking tackles (1-2 pts), and reaching the end zone (6pts). I reached third string after one week of practice, and reached first string by the end of the second week.