Build forearm muscles with wrist curls
Build forearm muscles with reverse wrist curls
Do hammer curls
Do farmer’s carries
Do dead hangs
Use grip trainers
Use thick-handled bars or grips
Do plate pinches
Train forearm pronation and supination
Increase overall upper-body muscle mass
Maintain a calorie surplus if gaining size
Eat enough protein
Progressively increase resistance
Train consistently over time
Accept that wrist bone size is mostly genetic