How can i make arms more hairy
By shaving them. Its the same concept as cutting your hair and removing the dead ends. Your hair will grow faster, thicker and healthier, although I have no idea why you would want to make your arms more hairy. Its not an attractive feature.
Eat more Bananas!
That's funny! Most people want to make themselves less hairy. :)
like Collins said
I dunno rub Rogaine on 'em or something...