Well, obviously it's best to start with lower distances. For absolute beginners, something like 40-50 yard sprints (or "as fast as you can go") is generally a good place to start. More rest between sprints is good too.
But for someone wanting to begin to up the sprint distance... starting at a distance with which you're comfortable (e.g., 100 yards) is a good point. First session, do enough sprints so that you're in the neighborhood of 1000 yards (the upper limit for a conditioning session length-wise, per Jason Ferruggia). Take two minutes between sprints. If that's too easy, take the rest periods down. Keep in this vein until you reach the point where sprints are followed by 45-60 seconds rest. If you're crazy, you could go to 30 seconds but generally that's not necessary. Once you reach that threshold, move up 25 yards. So, you'd aim for eight 125-yard sprints. Start with two minutes' rest between each, and then progress. Once you get to the one minute rest, move up to 150. Do six or seven per session. etc. etc.
But as your distances get longer, let your initial rest period get longer. If you get up to 250 yards, try resting for three minutes or so the first time. Once that becomes easy, then begin to tone down the rest periods. By the time you get to 400 yard/meter sprints, you'll only need about 3 (maybe 4) sprints per session with a few minutes' rest between each.