First things first Dressage is training so any/all training is a good thing. Don't get over anxious about showing, he can't show until he's 4. If your not a trainer he needs to go to one. You need to go to one. Read,watch,question- start learning everything. His basics will be balance, straight lines are the hardest so do lots of circles[large then smaller], change of direction,transitions[try by just looking up to get him to either slow or change gaits] and just becuase he is going to be a dressage horse take him outside the ring-sights,sounds,footing. Here is a saying you can use at all gaits -tick-tock-tick-tock-tick-tock-goes the clock. Say that in your head or outloud his feet will/should hit the ground on the same word consistantly=rhythm,no matter which gait. PLEASE don't try to pull his head in/down to put him on the bit. His outline as a youngster should be very natural, as training progresses his neck/head elevate, and at no point should his face be past verticle-a line drawn straight down his nose should always be slightly in front of that line. Think of a motor in the back[haunches] use the reins only to contain that energy, the more energy you create, if not allowed to flow forward will start to arch up. Sounds technical but really not to hard.Good luck