To improve your presentation of a dressage test try breaking it down and rehearsing each movement separately. Reduce it to its individual components, focus on perfecting each bit, then build it back up.
For example a recent test I rode had:
14. EK Medium Walk
15. K Collected canter left
KA Collected canter
16. A Down centre line
DE Half pass left
17. ES Counter canter
SM Change rein in collected canter.
Instead of trying to ride the movement as a whole I first practiced a walk/canter transition at K on its own until it was good. Then I forgot about that bit and cantered down the long side and practiced good straight turns onto the centre-line until I was happy with that bit. I then rode the second half of the movement missing out the half-pass (riding it as a straight line instead) – so down the centre-line at A, straight line DE, counter canter ES and across the diagonal SM.
Once that was good I put the half-pass in, and only when all of that worked well did I go back to the beginning and run through the whole movement starting with the medium walk.
Breaking down the elements this way to practice them and working on them slightly out of order also helps with a horse who is inclined to anticipate.
