Consider the sources of vibration.
1. Transmission: you have a chain drive motorcycle, adjust your chain, keep it well lubed (insert lewd comment, laugh, grin here) and replace.
2. Engine: You have an inline 4. Buy yourself a Morgan Carbtune, do a throttle body sync. Do it at idle set correctly between 1100-1300 rpm and at 4000 rpm. When the all four cylinders are firing in sync the engine produces less vibration.
Consider the structural components of the motorcycle and their effect on vibration.
1. Bars, Grips, and Bar Ends: All 3 of these can be set up in such a way to absorb the vibrations generated by the engine and transmission. Heavier bars or filled with BarSnake or sand or silicone, gel grips and heavier bar ends
2. Checking the torque on the engine mounts
3. Checking the alignment of the wheels
Consider the anatomical position of the body
1. Hand/Wrist position: You want the levers and angle of the bars to be in such a way that the wrist is neutral. When the levers are too high the wrist and hand are dorsi-flexed, causing constriction through the carpal tunnel and potentially irritating the nerves there.
2. Neck/Shoulder complex. The nerves of the hand originate from the cervical spine (neck) and pass through the anterior (front) part of the shoulder in what is called the brachial plexus. Depending on the riders history, previous accidents, age, injuries, work activity, etc. There may be some level of cervical degenerative disc disease, cervical radiculopathy, osteophyte complexes, braxial plexopathy, etc coming on. Physical therapy, neck strengthening and shoulder mobility can help free up the cause of the nerve irritation.