So, I've been looking at a lot of pony fan artwork and I can't help but notice that pony legs seem to do some pretty crazy things.
Someone already uploaded a great tutorial on how to not break a pony's leg, but I want to address what movement positions pony legs can and can't do.
So here are the first two gaits, the walk and the trot. MLPFiM ponies do a lot of these two. Trotting is very unnatural for real horses but what is even more unnatural is when people draw ponies with both legs on one side moving in the same fashion. That type of movement is called pacing or racking and takes a lot of training to achieve and even then horses cant always sustain it for long periods of time.
I'll post the canter and gallop in another submission.
Hope this helps.