lots of transitions and surpintines
I put poles in the centre of the school and work using circle over the pole and changing and getting the bend over it
Lots of bending, stretching, loops, circles, leg yielding in and out of a circle, cavalettis and poles,especially in a fan
turn their head tight and left until they put they're head down for a second then give them praise. another is to turn their head one direction toward you leg but not to far and hold their head there until you can see the tension in their neck decreas/disappear. Then go on the next side. If this doesn't happen for over 30-45 seconds give them a break them re try
But make sure to give your horse breaks between exercises and let him stretch on a walk, an extended trot or a frontwards and downwards neck.
Lots of circles, serpentines, figure 8s and lateral work, especially shoulder in.