My current favourite is the rice bath. It encourages composite wrist and hand movement, it facilitates all grip and pinch types, and there's a sensory component to it as well which may assist with proprioceptive feedback. The key is variation regardless of what you prefer. Use a ball, but also use a rope, or encourage wringing of a wet towel. Isometric holds of a barbell will build hook grip strength, but hanging from a chin up bar will encourage cylindrical grip. Remember that there is a clear correlation between grip strength and shoulder stability(3). Work in pronation and supination, sitting and standing, shoulder abduction and flexion.
Look after those fingers,
(1) Duncan S. et al. Biomechanics of the Hand, Hand Clinics 29 (2013) 483-92
(2) Landsmeer J. Power Grip and Precision Handling, Ann Rheum Dis 21 (1962) 164 (3) Horsley I. Do changes in hand grip strength correlate with rotator cuff function? Shoulder Elbow 8-2 (2016) 124-9