There are many things that you can do to ride a horse safely. One of the most important ones is to ride with a helemet. Especially if you dont even know the horse your riding. One of my biggest things on riding safety, is to ALWAYS ride with someone. I have had one of my really good friends out riding around by her self when her horse spooked at something she fell off but her foot was caught in her saddle's stirrup, and she was being drug, kicked in the head over and over as the horse was galloping off. Luckily she was wearing a helemt ( another good way to be safe.) Since no one was with her when her horse finally stopped she was uncontious and bleeding very badly, an hour later someone finally found her and was able to call 911. So i always make sure that someone is watching me ride, or ride with somone. Make sure that you also have boots on, if you were to wear tennis shoes they have that real grippy footing on the bottom, which could cause your foot to stay in the stirrup if you were to fall off. And you dont want to wear flip flops either, one its a big safety "no no" when your on the ground as well because you can easily accidently get stepped on and break a toe. and when your riding if you were to fall of, you could break your foot easily. One of my last safety tips would be to make sure your girth/cinch is around your horses belly tightly, otherwise your saddle may slip off the side of the horse and off you go!