One way to identify the muscles that you need to use for the leads is to have a partner attempt to move you while you resist like a statue. If someone attempts to move you to your left, those are the same muscles you need to engage to move your partner to your right. If someone attempts to push you back, in resisting, you use the same muscles that you'd need to walk forward.

Start with your partner applying a lot of pressure and then gradually reduce the pressure while still making sure you can feel which muscles are firing. Mostly, it should be the same muscles even as the pressure lightens.