Blow out your BIS with barbell curls, super setting inner and outer grip with a training partner. Get a low weight and start with outer grip and do 10 reps. Pass the BB to your training partner and he does 10 reps inner grip. He passes the BB back to you and you do 10 reps inner grip. You pass it back to your partner and he does 10 reps outer grip. If you guys can keep going then keep going. It doesn’t matter if you start inner or outer as long as you are swapping each time. You can also do this on your own, it’s just harder because there’s little to no rest between changing grips.