Establishing the Layout Lines:
It is critical that you establish accurate working lines. You are creating a kind of a map to follow to assure an attractive, quality job. All working lines should be bold and easy to see. What you are seeking is a layout that enables you to lay your tile so that there will be full size tiles in high visibility areas, and all edge (border) tiles are at least 1/2 tile or more.
First, make a dry-run for the layout by running dry tiles out from the two most visible walls to see which would work best with your room.
If the tiles at the end of each row (border tiles) are less than half a tile width, adjust the row by moving it the width of half a tile. This will assure you that all the cut tiles will be more than half a tile width.
Also, check to see that the corner that you are working off is square. If it isn't, tack battens to the floor that are squared accurately a tile width from the corner. Use a framing square and chalk line for this process. The line closest to the wall is established by snapping a line one tile length away from the wall along both walls that you're working off of. Then snap another line parallel to it that is the thickness of two grout lines. (This way you are allowing for the grout line along the wall and for the next row of tiles.)
Then nail battens made from 1x2's or 1x3's along that working line so you have a firm position to start running our tiles. Make sure your battens form a right angle and are straight.
Later, once the tiles are laid in the field, remove the battens and tile along the edges, cutting the tiles if necessary. REMEMBER, when you are cutting tiles always leave room for the grout line.