leg yeild is a great move to loosen up the horse, gain confidence, show him where he's putting his feet, etc. Start by warming up at the walk/trot and really loosen your horse up, do a lot of bending, counterbending, make sure they're paying attention to your aids, do some shallow serpentines, figure eights, transitions,just keep them relaxed and paying attention and doing their job as you ask them.
Come out of a corner and cut acroos the ring so your at an angle to the rail. Halt 5-10 feet from the rail (just guesstimate) you don't want to get too close to the rail just because the horse might feel blocked up if you do. then slight;y bend their neck to the inside, keep your inside leg on the girth, the other slightly behind and tap their side with the outside leg, ask gently at first then more firmly. you can use half halts and both legs to slow, then straighten them as needed.