Some good advice so far.
Seeing as how you feel biceps exercises near the crease of your elbow, I’m going to assume that you’re using mainly the brachialis when doing curls instead of the biceps. I like BONEZ’s idea about the contracting your biceps to be better at activating them. You could also just simply try to contract your biceps when ever you get the opportunity throughout your day (do it in private if you feel silly hitting a biceps pose in public) instead of making a specific workout out of it. The goal after all is to improve mind muscle connection/activation, not necessarily fatigue your biceps.
Another thing to try is to increase the supination component while curling. The biceps brachii perform 3 joint actions:
- elbow flexion (bending the arm)
- shoulder flexion (raising the arm)
- wrist supination (turning the palms towards you)
In order to do this you I’d suggest either using a barbell for 1 arm curls, grabbing dumbbells towards one side (towards the outside if holding the dumbbells with palms facing you), or if you’ve got adjustable weight dumbbells you can even weight the two sides unevenly (again, you want the “inside” to be heavier).
Then you can either just keep the wrists supinated, or actually supinate/rotate them while curling (obviously cannot be done with the barbell option).
Because only the biceps perform supination, and none of the other arm flexors, this will increase biceps involvement in the movement.