Walking 256 Steps
Self Explanatory, really.
Any vitamin will increase a Pokemon's happiness. The vitamins, if you didn't know are the HP Up, Protein, Iron, Calcium, Zinc, Carbos, PP Up, PP Max and Rare Candy. If your friendship level is below 99, it will raise by 5. If it's between 100-199, it will raise by 3. If higher than 200, it will raise by 2.
The friendship level will raise just like it would if you used vitamins.
The EV Berries are the Pomeg Berry, Kelpsy Berry, Qualot Berry, Hondew Berry, Grepa Berry and Tamato Berry.
You can also trade to FireRed and LeafGreen to get grooming from Daisy, which will raise by 3.
If you give your Pokemon any herbal medicine, it will decrease depending on what herb it is.
If you want to track your progress, you can head to Verdanturf and in one of the houses you will find a woman who will rate your friendship. Here's what she will say:
"It adores you. It can't possibly love you any more. I even feel happy seeing it." 255
"It seems to be very happy. It obviously likes you a whole lot." 200-254
"It likes you quite a lot. It seems to want to be babied a little." 150-199
"It's getting used to you. It seems to believe in you." 100-149
"It's not very used to you yet. It neither loves nor hates you." 50-99
"It's very wary. It has scary viciousness in its eyes. It doesn't like you much at all." 1-49
"This is a little hard for me to say... Your Pokémon simply detests you. Doesn't that make you uncomfortable?" 0
^^ All that friendship rated stuff from Bulbapedia.
Check frequently to get an exact rating of your progress. Of course, 256 step will detain you from getting an exact rating, remember.
Good Luck. Hope I helped. :)
Source: Above Link