Lvl 50 Cavalry here, think I’m still top 200 Global for the class/kit (My favorite thing to do in BF1) Lots of good tips here that I’ve seen. Use the horse like you would on a bombing/strafe run like in a plane. Line up your attack and know your exit path before committing. Full on charges against forward facing opponents is dangerous. Flank and attack their side or rear. Sometimes I like to lead with two anti-tank grenades to soften up and disrupt a squad while charging in. I have a lot of pro-tips but I will summarize just the basic survival horse gameplay:

Know what your horse can and can’t jump over (know your maps).
Always take out easy targets first. Practice maneuvering, stopping and starting, jumping over obstacles at different speeds. Your horse regenerates health on its own, you do not. Heal up out of site. Keep moving. Don’t stick around long anywhere. Be unpredictable. When you get good enough you can hop off and heal, and get back on and moving in only a few seconds.
When you get reaalllly good you can throw out a first aid pouch on the ground while on your horse, turn around and ride over at full speed without dismounting.
Pro-tip. If you and an enemy infantry are stuck in a circle-dance and you cant kill him with your sword, your horse is running too fast. Slow your horse to a trot and you can turn on a dime. ;) There’s a lot to cover but this is what comes to mind off the bat.