Hair grows a half inch per month on average for most people. There's not much that can be done about this as it is just genetically determined. There are multivitamins specifically formulated for healthy skin, hair, and nails, but I wouldn't expect much from them as long as your diet is reasonably healthy. If you're getting less than a quarter inch of growth per month or recently noticed a sudden slowing of growth that might be reason for concern but otherwise growing hair just takes a lot of time and patience.