I have a few questions about laying tile?

I am in the middle of redoing my bathroom and I've gotten to the tile portion. I have never tiled before so I asked around to find out the best way. I've gotten two different answers. One is to just put morter on the wall and apply the tile (with the proper trowl), the other is to put the morter on the tile and wall in a criss-cross patern. I've been told that it holds better to do both and I have also been told that it is too much morter when doing it that way. Any help in this delema would be appreciated.