So...I hear people say all the time to not use human stuff on the horses... but I ALWAYS do. The trick is that you have to make sure that you get it all rinsed out of thier coat. If you leave any soap at all, you can get an skin rash.
Now, conditioner is a different story. I tend to used whatever I have, but you can leave some of it in the coat. It works great as a fly repellant and makes the next several times you work the tangles out of the mane and tail much easier. I will usually condition the whole horse, rinse it all out, then use a really really deleated bit of conditioner (about an ounce of conditioner in two quarts of water) and then splash the horse with it. But, you have to let it dry on the horse.
Ok, fly repellent asside, lets talk bathing.
When you get the horse in the wash area, be aware of how you put the water on him/her. Most horses like the water warm to very warm. Start with a calm stream of water on the hoof itself and see how the horse takes it. If they freak out, back up and teach them to take water.
If they don't freak out, work up thier leg to the body and you can turn the water to spray if you want. I usually start at the high neck and rince down that whole side of the horse. Soap up that side of the horse, rinse, condition, then rinse twice more. To the other side the same way.
Wash the mane and tail - making sure to leave conditioner in the tail for several minutes.
Rinse the whole horse (less the head) twice more. Make sure to include the sheath or udders in your cleaning.
Some horses will tolorate water from a hose on thier face, most won't without specific training. For those horses, I use a sponge to clean thier face. Make sure to rinse all possible soapy water from the horse's neck.
At this point, if you want a clean horse, use a scraper - metal or plastic - to get the excess water off and tie them until they are completely dry.
Now, here is the sad part. My horse is a pinto who is 70% white. His skin is pink and when it is clean, he sunburns at the drop of a hat. Twice a year I do the above scrub down - all the way down to pink skin. I let him dry with his conditioner rinse. Then, just before I put him back in his paddock, I give him a complete rinse and put him out dripping wet... At that point, my white horse rolls in the dust and becomes a brown horse... but with a new coat of dust over his skin, he doesn't sunburn.