I'll give you a couple of exercises given by Rolex Eventers.
I've cliniced under Dorothy Crowell countless times, who represented the U.S.A at the Olympics for Eventing and is a CCI**** and CIC**** Eventer.
The top one teaches control, this one teaches rhythm - and you really find out exactly how precise of a rider you really are.
You start out with the poles on the ground, and then work on keeping the shoulder under, keeping the rider centered and balanced with a secure seat and tall upper body.
Working on straitness, roll backs, preperation, control.
Then you merge into trot with the poles on the ground - same thing and then merge into canter with the poles on the ground - same idea.
Then move the poles to x rails and etc, etc, etc.
Then you can also add fences aftarwards.
The 2nd, was given at a clinic under David O'Connor. Everyone knows who David O'Connor is *grin*
This one, same idea - but you can incorportate bounces and corners as you would find in mid levels of eventing.
Here are some vids to help understand.
These were taken 4ish years ago....so no laughing *phtpth*
Also - the quallity is horrible....my appologies... My Videos :: NelsonandZeus065.flv video by Laya01 - Photobucket