Before performing any resistance training exercise, I teach my clients to get in the right position first, which is referred to as “neutral spine” or standing with good posture. The upper back and abdominal muscles should be tight. The feet should be under the knees which are under the hips. Make sure you chose a weight that you can control for the repetition range you are using.
Place the elbows slightly forward to keep the load on the muscle throughout the whole set. As you flex the elbow joint, avoid leaning back (see photo). The concentric contraction is complete when the arm is flexed at the top of the movement. Make sure you lead with the wrist, instead of the fist. In other words, avoid moving from the wrist. Keep it straight..
When you are returning to the extended elbow position, keep your upper back muscles engaged, so the weight does not pull you into a hunched position on the way down. You may even want to try the bicep curl with your back up against a wall to minimize any swaying of the body.
Do a full range of motion, without relaxing the bicep muscles at the bottom, between repetitions
For exercise videos, go to https://freedomoffitness.com/gallery/.