How do I get my horse's hindquarters working properly in leg-yield?

Does the horse tend to "run away" with the forehand, so the hindquarters end up trailing a little and the sideways movement is not quite correct? Or is your question more about what a correct leg-yield looks like?

If the hindquarters are trailing, it helps to ride a few turns on the forehand first, to work specifically on moving the hindquarters across.

When it comes to the leg-yield itself, it is worth remembering to match the forehand to the hindquarters, not the other way round. So rather than thinking that the hindquarters need to "catch up" with the forehand, the forehand needs to wait for the hindquarters ☺️ In other words, as the rider, remember that it is the forehand that "runs away". You counter this above all with restraining rein-aids on the outside rein 🌟