Can you water the arena so you can see your tracks?
QH gave you some sound advice. Stay balanced, look up, do NOT put weight to the inside or the outside. Stay centered. Hold your rein pommel width apart, if you're in a snaffle take contact and if you're not in a snaffle, get in a snaffle. Here are the roles of your two reins:
Inside rein: Keep the horse from diving in, keep the horse from blowing out, keep the horse gently bent, lift the shoulder.
Outside rein: Keep the horse from diving in, keep the horse from blowing out, helping balance.
Now both reins should remain with the same amount of pressure. Both used to get the vertical flexion in his nose and to keep him balanced. Hence they both keep the horse from diving in or blowing out. Squeeze with your legs until you get the hind end engagement; maybe a little more inside leg to encourage the horse to soften his rib cage.
Finally, all these things together....Look up, keep the rein pressure steady, inside leg for bend and outside leg to keep from bowing. Try and get a watered arena so you can see EXACTLY where you are tracking. Nothing makes me happier than seeing a perfect circle in wet sand.