Here- I hope this helps.
1. The face
Horses have a almost square head the gets thinner towards the end, they have kinda large eyes.
2. The muzzle
A horses muzzle says a lot, a wide square muzzle is for bulkier breeds where a thinner softer muzzle is more Tb and sports horses, the nostril is the same ratio as the muzzle.
3. The legs and chest
Horses have a rounded chest with a lot of muscle, use simple shapes to make up your horse.
4. The Neck
Like the muzzle, choose what type of horse you are drawing, a longer thinner neck for sport and a shorter fatter neck for drafts.
5. The ears
The ears are placed where the head and neck meet, make sure they are the correct size for the horse.
6. The mane and forelock
Make sure the mane always points towards the earth unless the equine is making the mane move.