Before even that, have you checked the floor structure to verify it is strong enough for tile? It's often easier to tile the floor then the walls because you don't have to be as neat with the tile cuts at the walls - the wall tile will cover those. Note, do not tile to the wall, leave a (small) gap and do NOT grout it. The tile needs some room to expand. If you want to avoid caulk at the joint there, www.schluter.com makes some expansion joints designed for wall/floor transitions. Then, it doesn't matter which goes first, since each edge needs to be visible.
Check out www.johnbridge.com for tiling help.