Hello Vskerche,
The general rule is "nothing smaller than halves". Ideally, you'll want your layout to result with all of the perimeter pieces being larger than half-tiles. If you have the tiles on hand, lay them out with your chosen joint width to compare how these variations will work for you. Yes, if I can work out a full tile at the focal points of the room, that's what I prefer to do. That's not always a possibility though.
I've found that using Photobucket.Com to host your photos, and then posting the HTML code here, has worked very well.
Shaughnn

Shaughnn,
Thanks for the reply..here are a few pics of the bathroom and a few trial tile layouts..Hope they load

first a full view of the bathroom with the symetrical layout (will have approx 5.5" tiles on both walls) apologies for the blurry pic

45 degree layouts (notice less than full tile in front of shower

45 degree layout at door threshold. 1/4" grout lines..Thinking of going up to 3/8"

With the straight layout, I'd move it all over a half tile, and then you'd have pieces 11 1/2" +/- on each side. As for the diagonal, I'd be moving it all over about an inch to the left, so as to have full and half tiles against that wall (that's the one you're going to see), and then cut in what ever you get on the other wall. You're going to have the toilet and vanity over on that wall, so most of it's going to be hidden, anyway. Additionally, it'll give you a bit bigger piece in front of the shower.

One other thing-- at the door, I'd leave it exactly as you have it now, and either put a straight piece across the door, or use a marble threshold, and just cut the full and half pieces to it.

Thanks for all the follow up..Excellent suggestions. I played around with the layouts all day Sunday and have it set now. I'll be going with the diagonal pattern you see in the last two photo's above. What I did was slide full tiles up against the shower base, laid out my tiles and found I could get a full tile at the door threshold, but it was about 1" away. From there I went to 3/8 grout spacers, and moved the tiles 1/2 from the shower base. With that move I can get to within 5/8" of both walls (where I will have 3/4 baseboard + roundover) and the tile at the door threshold meets the carpet line. I'm going with a Schluter transition strip at the doorway. All my small tile cuts will be at the far wall. One quick follow up question, there are a few uneven spots in the floor (tile rocks about 1/8 - 1/4" Will the standard 1/4 x 3/8 trowel be ok, or would a 1/2 x 1/2 be better? Tile is 13"

1/4x 3/8 should work fine. Are you sure it's the floor, and not possibly a screw or nail head? If there's that high a ridge in the floor that a 13" tile will rock 1/4", maybe a 1/2" notch wouldn't be such a bad idea.

Here is my final layout. 45 degree tiles with 3/8" grout lines

Full bathroom layout

Bathroom Door Threshold..Got a full tile to fit (YEAH)