To make it sttronger give it protein, calcium, Hp up, iron. Also if its hp goes low give it potions that makes it happy (use potions because every potion, super potion, hyper potion gives 1-3 happiness points and go to the poke center gives nothing). And how pokemaster said give it the soothe bell, if you them whit the luxury ball will be easer to grow its happiness (luxury ball duplicate the happiness points you get). I hope it this is usefull.