Not sure how this competition works.
If you get a ranging shot or two, it'll make life a lot easier.
If you have the chance to adjust the scope between targets, then zero at 200yds and learn the number of clicks you need for subsequent distances.
If you can't adjust the scope, zero at 200yds, then learn the target, where do you have to move your point of aim given bullet drop.
http://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi
Figuring out wind drift is the hard part.