Quarkrad

Apologies if this has come up before - about to tile bathroom, having just tilied floor. I have worked out where tiles will go including around window - jave primed walls and ready to go. Understand battens (horiz and vert) go up in lower corner and tiles laid in horizontal walls bottom to top. Question is: do I do one wall complete and go around the room or is it advisable to work on all 4 walls at the same time? What I mean is - one could go around all 4 walls on a horizonal base line so it all matches and then work up vertically. Not sure what professional tilers do. I'm guessing you complete one wall and then go around the room having drawn out a horizonal base line. One last question - assume you always tile bottom up. Read somewhere that you start 1m up from the floor but cannot see how you stop tiles slipping down. (I'm using quick setting, 3 hr, powder adhesive). Regards.