Lots of in hand pole work and backing up (in straight lines, serpentines, and figure eights). This is what my chiropractor suggested for my guy during injury recover!
I worked with a trainer who used Frank Bell's ground techniques with a natural horsemanship halter... learning "the dance" on the ground really improved my Paint mare's focus when she is under saddle. I have used it on an Arabian, a TB, a Morgan, my Paint and my future Paint filly will learn it as well.
Also, hill work in hand and in hand schooling over some xc obstacles can really boost your horses confidence before you try it under saddle.
Try teaching your horse the basics of moving off of pressure at the girth area. This will help with leg yielding/half pass under saddle. I also like to teach turn on the haunches and forehand on the ground first!