The standard biceps curl is hardest at the mid-range, where the lever arm is the longest. But for variety we can change that, making the top or peak contraction the toughest part of the movement.
Lean forward at a 45-degree angle.
Don't drop the elbows down. Keep the upper arm in line with the body.
Perform curls in this position, squeezing hard at the top.
Move slowly through 2-3 rounds of 5 reps on each side to prep the shoulder before your next pull-emphasized training day that involves things like pull-ups.