Research, research and more research; not the players or the PCs, me. Doing some research on horses for an article here. Boy oh boy there is sure a lot to read about horses.
I actually started out wanting to do a piece on jousting and was quickly distracted by the role of the horse . I've always felt the horse was given pretty short treatment in most rpgs. It's not a motorcycle that sits there and waits for you. It's a living being with it's own limitations and abilities. Not just an item on an equipment list. Horses should really be treated like an NPC. Horse traits in the 2nd edition AD&D DMG and the Hackmaster GMG actually are the best treatments on the horse as an individual and different living creature I've ever seen in any RPGs. But they leaveme hungry and wanting more information.
Historically horse is a prestige item, a necessity and different breeds and types of horse really have a big impact on what you can use them for. Thankfully my wife used to live on a horse farm so I was able to consult her and talk about horses for a while to give me a better idea of what I was looking for online.
The internet might give us a lot of dubious information but it is also one of the greatest gifts to DMing that ever came along. Now I just have sort through things and dance that line between Sim and Game, realism and fun. Sometimes it all requires a bit of research.