Basically the only advice I ever got before running my first open 400 last year was build on the curve, stride the straightaway, build more on the next curve, all out sprint. It's not like you have time to work on drills and get down 100% sprinting mechanics the day before you run the 400. Just don't go all out at the very start, because there is indeed pacing required on a 400. One of my team's 400 runner, who was an 800 runner (so he has more stamina than most of the guys) tends to go all out in the first 200, then is caught by like 3 other guys at the start of the last 200. Don't do that. You indeed have more strength than they do, but other people probably have more speed.