1- Grasp a barbell with underhand grip with shoulder-width apart, resting the back of your forearms on your thighs or bench.
2- Start by rolling the barbell down into your fingertips.
3- Now curl the barbell up so your palms face your elbows, and repeat.
Tips and Advices:
1- Make sure that your elbows and forearms remains stationary on thighs though out the movement.
2- Keep your hands in direct line with your forearms.
1- You can do the same exercise using dumbbells instead of barbel, but make sure not to overload weights.
2- You can also perform this exercise while resting your forearms on the incline pad of preacher machine bench.