Control the weight. Lock your elbows to your side and really focus on not swinging at all!!! Make the biceps take all the strain and really control the negative. Its amazing how many people rock the weight up and cheat curls without even realizing it... I use to be guilty of this. Lower the amount of weight and really focus on controlling it. I think you will be humbled by how little weight you'll be able to curl when you actually are 100% focused on strict form. Also, keep intensity high using drop sets, rest pause sets, etc. I would recommend only training them once a week unless you are on cycle. And unless you're eating at a calorie surplus theres no chance of them growing.