Let your legs go where they are relaxed. Some say heels under your hip. I feel most comfortable and balanced with my heels just in front of my belt buckle. I sometimes slide my feet forward because I find it an easy way to relax into the saddle and move with the horse...but once I get in synch with the horse, my heels slide back toward my belt buckle. Do NOT take lessons from a stranger
. Lots of riders don't know squat. Some would tell you I fall in that category. Don't take what I write as gospel either! For general purpose riding, a relaxed leg draped around your horse is pretty hard to beat. It puts you deep in the saddle, and has your legs around the horse for unexpected movement.
This is how I ride. I'm a nobody rider, but it works good for me & my horse. I'd like to get my toes more forward, but that is a work in need of a lot of progress:
My daughter in the background obviously takes a different approach. The saddle she is riding forces your thigh into a certain position. I hate to ride that saddle because of it, but she doesn't mind. Neither does her horse...