patgizz, what if a brotha' was considering doing it in a diamond pattern? Is that a 'first time out of the gate' type thing? I know a chalk line is the way to start (just like everything in building!), but to make it simpler I was thinking use a long straight edge (maybe a 6' aluminum or steel angle section) to get several of them at 45 deg to the walls, then build out from there.
Here's how I would layout a diamond pattern.
You haven't said the size of the room. Great room- I'm assuming big.
I don't use chalk lines when laying tile. I set nails in the edges (baseboard, etc.) and pull strings nail-to-nail about 1" above the floor, and leave them there while I work. I can lift them to spread under, and they pop right back when I let go. Chalk lines have a bad way of disappearing when laying tile, and it's almost impossible to re-snap halfway through the job (wet cement, tiles in the way, etc.)
It's very nice to start a long wall with triangular half cut-tile tiles, but I always dry lay a few lines of tile all the way across the floor to see how it will hit the opposite wall. I NEVER leave small tiles.
Of course, there are mathematical ways to lay out the room as well.
There are only 2 ways to layout a room- center a tile, or center a joint. One will leave small pieces at both walls, one will leave large. Of course, with a diamond pattern, is slightly harder, but same principle. The center line of the room has both the center diagonal line (corner to corner) laying on it, and the corners where 4 tiles come together (alternately).
On more trick... 45 deg with a straightedge isn't all that helpful. It's pretty easy to be 47 deg or 42 deg, and be messed up when you get to the other end of the room. However, go back to the strings. If you measure from a 90 deg corner in 2 directions the same dimension (regardless of what it is), connect the dots, and you've got a 45 deg angle. So, after dry fitting a few tiles to see where you want your joints to lay, copy the dimension to the adjacent wall, and connect the two points with a string. This line will be your diagonal joint line.
Did that make sense, or am I talking gibberish?
Okay, I think I got it.
The room is rectangular, meaning a string line going from corner to corner won't provide the correct 45 degree angle. So, Cliffs Notes version:
1) find the center of the room
2) run two 90 degree lines which intersect at that point, one lengthwise and one crosswise
3) run my 45 degree line from the 90 degree line. And I can do that mathematically, too. 
I dry lay my tiles to see how it's going to intersect the sides of the room. FWIW, I prefer the room to look balanced, so I'd prefer to have the side tiles as near the same size as possible, meaning I'd need to move my start point as needed to account for that.
Close? Or is it back to school time? <img 
makes sense to me but thats how i do diagonal floor layout too.
for diamond pattern walls i start off a level board and work from there. actually for all wall tile i start off a level board then fill in to the floor later unless the floor is dead level.
here is a bathroom i did for a customer.
and this is the schluter kerdi membrane mentioned by someone else, installed over cement board below the tile
Curmudgeon wrote: Okay, I think I got it. The room is rectangular, meaning a string line going from corner to corner won't provide the correct 45 degree angle. So, Cliffs Notes version: 1) find the center of the room 2) run two 90 degree lines which intersect at that point, one lengthwise and one crosswise 3) run my 45 degree line from the 90 degree line. And I can do that mathematically, too.
he meant find a 90* corner and measure out X from there. say 8 feet each direction and string between the two points. not string corner to corner.
Ah, okay, that makes sense. I was under the impression you should always start at the center when tiling?
like this
dont need to start at the center if you do your layout correct, then you can start wherever you want. like working outward toward the door so you do not tile yourself into a corner.
Yeah, I'd hate to be stuck in a corner where I couldn't get to the fridge. BTW, that bathroom looks fantastic!
In reply to Curmudgeon:
Either of those methods will work fine. Both were much better explained than I did.
If you get your brain around it, diamond layout is actually easier than straight, because there is only one way to do it.
If you look at the back wall of patgizz's shower, there is a row of tiles centered in the wall (that is, the top corner of the tile and the bottom corner of the tile both fall on the centerline of the wall). This leaves balance at the edges. However, the next course is the opposite- the grout corner lands on this same vertical centerline (the right and left hand corners of 2 adjacent tiles are on the centerline). Again, when these reach the walls, they are balanced.
With diamond layout, there is no way to avoid small tiles at the edges. It is a factor of the dimensions of the room.
In reply to Curmudgeon:
Lots of good info here. I did my basement in ceramic over slab. I have a complex sort of Z shapped room and several closets, and spent days measuring and drawing layouts to minimize small pieces at the edges - found an online tile layout calculator that helped to get me close. I also laid out the tile dry and did a final tweak of the layout - all of that work was worth it. Installation is hard, tiring work to do yourself. I laid all full tiles for several days, then rented a saw for the last weekend to do the cut tiles. It would have gone a lot quicker with help and definately one to cut, one to install is best. I had some uneven spots in the floor (drain lines) and did not use a leveler and I probably should have. I used the mortar to level a bit, but still have some uneven tiles. Spacers are a great guide but definately tweak a bit as needed to keep the tiles looking even. Also, I decided to remove and replace one tile that I didn't get all the air out from under when I was trying to level over an uneven spot - I spent hours breaking that one tile up and removing the mortar - it really bonded well to the concrete in most spots. Last suggestion - go slow and inspect your work as it dries to make sure you didn't accidently shift a tile - they'll move back in place for awhile.
klb67 wrote: It would have gone a lot quicker with help and definately one to cut, one to install is best.
That's a really good point.
When you are installing cuts, do everything you can to stay on your knees. Teach someone else to cut and haul the cuts back and forth (since your saw will be outside).
Getting up and down will completely wear you out.
SVreX wrote: Getting up and down will completely wear you out.
:)
You want to be wore out after a tile job... try one with me sometime..
I do all my layout pretty much like you describe.. but I WAS a chalk liner.. I am trying your method of leaving a string next time
But what will wear you out working with me.. I am a speedsetter... :)
I ALWAYS have a bag of the quick setting mortar on hand. For something like a 12x12 room or smaller I can typically be DONE in well under six hours.. Grouted.. cleaned up.. DONE...
I first lay out the whole room with methods like ya'll are talking about.. Maybe make a few cuts or two if possible.. Or needed..
Then starting at the first area needed to walk on... I tile away with speedset. YES sometimes this tiles me into a corner, but none of the cuts have been made and the stuff is setting fast... Then I tile the entire floor save the cuts..
Next.. clean up.. take a break.. Let the stuff fully set.. Ect.. Then go back once set... (about thirty minutes or less) and mark all the cuts.. Numbering them around the room... Carry the big stack of cuts out to the saw... and cut away...
Test fit all cuts.. Then back butter... and stick..
Eat a snack..
Grout.. Done..
Even for big Floors where it doesn't make sense to work your butt off using big batches of speedset.. I still almost always lay myself out a path in speed set so I can come back and work.. I dunno.. It just seems to work for me....
and I guess you could do all the cuts last method with regular ole thinset. Just however you go about using that method.. You must be careful not to squeeze to tight into the spaces you are 'skipping'. Layout becomes just a bit more critical to a quality job.
Even in one of my fast jobs.. I don't hurry through a layout. Rushing that wastes time :)
^^OK, I'm impressed.
The only thing that hasn't been covered so far in this highly informative (and GRM-typical) thread: radiant heat under the tile. Seriously. I know Charleston is damn near subtropical, but tile is COLD and it sucks heat out of the whole room. Radiant heat is really pretty cheap, very easy to install, and it has the potential to make the whole house more livable, even if you only need it a few days a year.
Especially in a room that gets lived in like a great room, I don't think I'd lay a floor again without it.
I'm inland now (Columbia), it still gets every bit as hot as Chucktown, sometimes hotter. In the winter it can get into the teens at night and once in a great while down into single digits.
I will usually throw a rug or two over a hard floor (unlike carpet they can easily be cleaned thoroughly) and am happy.
ronholm, I like your method. Get in, get done, get out.
For the dollar/awesome ratio*, you'll have a really hard time beating a radiant floor.
*At least with stuff that doesn't go BANG! or ZOOM!
In reply to ronholm:
I am also pretty fast... but I can also organize a cutter very efficiently.
I never save the cuts for last. I START someone cutting at the same time I start laying tile. My helper sets up the wet saw and mixes the first batch of mud WHILE I am laying out the job. By the time he's ready, I know enough cut sizes for him to start with. There is no point in worrying about starting in the middle, or getting stuck in a corner. I simply cut and lay as I go, and work toward the door.
That way 2 12x12 rooms can be done in a day! 
Actually, I don't do too many 12x12's any more. Most of my work is pretty complicated.
I used to do production tile work. Hotels, etc. When there are hundreds of rooms to do, you can't keep up if you can't knock out 8-10 tub surrounds per day.
In reply to SVreX:
Your hired!
With a helper the game changes slightly 
Ya ever run into Chuck Heckman doing hotel work? Standard improvement company?
SVreX wrote: In reply to ronholm: I am also pretty fast... but I can also organize a cutter very efficiently. I never save the cuts for last. I START someone cutting at the same time I start laying tile. My helper sets up the wet saw and mixes the first batch of mud WHILE I am laying out the job. By the time he's ready, I know enough cut sizes for him to start with. There is no point in worrying about starting in the middle, or getting stuck in a corner. I simply cut and lay as I go, and work toward the door. That way 2 12x12 rooms can be done in a day!
we must have gone to the same tile school, because thats exactly how i do things. my helper is a very good tile cutter and can keep up with me. we'll knock out a whole kitchen and bath with wall tile and tub surround in a day. the last tub surround we did was 4x4 tiles on sheets of 9. it came out from the back wall 3 feet so the only cuts were for the edges of the rear wall and along the ceiling, that was done in under 2 hours.
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