Personally I believe looking for a good conformation and good attitude and behaviour are some of the top things to look for also when/if you test ride the horse, just making sure you feel comfortable and that you and the horse are getting along well!
Hope this helps
I had many experiences about it but will you be looking with a dealer?
Try lots of different horses and don't decide for one until you you find one that feels right. Never choose a horse for its appearance. The one that'll feel the most right is the one to choise, even if it looks like an camel, maybe it jumps to the moon or does flying changes like no other horse. What I want to say is give lot's of horses the change to bewitch you. Sometimes the horses that stand out screaming "I am a superstar" are the most nasty ones to be stuck with and sometimes the underdog is the one how takes your breath.
And they have one extra point buy being cheaper than the first group. Maybe the first horse you is the one, but that's most of the time not the case, maybe the fifth is, or the twentieth.... Hope that helps and good luck .