Eat more calories then you need, heavy emphasis on protein. Then you need a good weight lifting routine also, for building mass you want to work your back and legs to put on some mass. This is my 5th week of 5x5 and my Quads are starting to show up some more, and my back is looking better. But I'm cutting.
You can clean bulk or dirty bulk. Difference is, clean is a diet where most if not all foods are healthy, dirty is where if it has calories, you eat it.