A rearing bit is commonly used in racing stables to provide additional control of the head.
Sometime horses will try to pull their head towards one side or the other to avoid going into the vehicle.
The rearing bit can help you keep the head straight.
A nose chain could be used instead of a rearing bit to keep the head straight.
There are several types of halter that are designed to discourage the horse from pulling backwards.
They work by putting pressure on the poll if the horse leans back.
The pressure is released when the horse steps forward.
A whip can be used to touch the hindquarters or legs to encourage the horse to move forward or to keep the horse straight.
The whip must never be used in anger it is more an extension of your arm and allows you to touch the horse without getting into kicking or trampling range yourself.
A lunge rein can be used to make a breeching rope or for cross behind the hindquarters to encourage a horse to move forward.
A wide and thick rope is safer and it is a good idea to use gloves when you use ropes to prevent rope burn.
Some people like to use feed to encourage the horse into the vehicle.
This rarely works with a nervous horse but it is good to have on hand to reward the horse once it has loaded.