Plan tile layout first
When tiling a whole room, the layout should be worked out before fixing any tiles with adhesive.
This can be done by considering one wall at a time, but the base line must be worked out for the room as a whole.
Tile levels around windows and doors
When establishing this base line for the wall tiles, consider the levels of windowsills, door heads and other items such as bath top and worktop levels.
Probably the most effective method to ensure good results is to draw each of the walls to scale on paper and to map out the alternatives.
When setting out a whole room, ensure that the horizontal line around the base ties up at each of the corners before fixing the base batten. Tiling which steps up or down at the corner can look awful.
Tile grids
Draw each wall to scale on paper.
Using the same scale, draw out a grid of tiles on tracing paper or acetate.
By holding this grid over your scale drawings, you can assess the best position for the tiles.
Remember though, that the horizontal lines will need to be matched up on all the walls!