My own personal superstitions:
If a horse breathes on you it is good luck. If a horse yawns at you, bad.
Hold the bucket wile the horse eats he will appreciate you more
It's bad luck to leave knots, braids or elastics when the horse is turned out.
Bridle last, unbridle first.
To cut a horses mane with scissors or clippers, is unlucky, with shears, lucky.
Keeping a lock of your horses hair near you, or near where you sleep, is good luck.
Letting a horses chestnuts grow is bad luck, they should be peeled regularly.
Tie a horses tail in a war knot before going on a trail ride for good luck: Picture 054.jpg