Lots of food, healthy food that is and heavy compound lifts. I put on 10kg over about a few months that way, I'm 80kg now. I wouldn't bother with creatine but thats just my opinion.
Theres no real science to it, eat a lot, lift heavy and rest a lot.
Read
http://www.sherdog.net/forums/f13/s-...e-read-436935/
and this
http://www.sherdog.net/forums/f15/at...-s-faq-718093/