Ponies are basically a stationary step-ball-change. When I think of ponies, I always think of the musical Hairspray.
www.youtube.com . . . (in the link, they do ponies as the beginning to several phrases...I would guess 60% of the music in that show can have ponies done to it).
Think, start with your weight in your left foot. There are 3 parts to a pony.
1) You step completely onto the right foot, and keep your left foot close to your right ankle.
2) You put your left "ball" on the floor, and straighten your knee which will cause your body to rise up a few inches and thus your right foot will raise off the floor a little because your left foot is accepting most of your weight.
3) You bend your left knee, which causes you to step back onto your right foot completely.
Then, do the same thing to the left. (Edited to add this) As with many steps in dance, it's not complex to execute, the trick is getting it in your muscle memory. That just takes some practice...and some repetition. Spend some time at home doing it slowly and as you get more confident speed up a little bit, and when you get confident with that speed up a little more. I have probably done 100,000 ponies in my life and I don't even have to think about it anymore...you'll be the same. Try not to stress about it...you'll figure it out!