Working with tile for a patio begins with laying out the concrete slab.
If you have an existing slab and it's in good shape, the right size, and in the right location, you can tile over it. If you don't have a slab, you'll need to pour one.
To tile an old slab, lay out tiles without mortar first to center the pattern so the edge tiles will be the same size. If you're tiling a new slab, plan the slab size so that it won't require any cut tiles.
In either case, use thinset mortar mixed with a latex additive -- it is stronger than water-mixed thinset. Mix only as much thinset as you can use in half an hour. Use a drill with a 1/2-inch chuck equipped with a mixing blade and mix the mortar in a 5-gallon bucket. Mix thoroughly, let the mortar stand (slake) for 10 minutes, then mix it again. Work in sections small enough that you can lay all the tiles within a section before the mortar sets up.
When installing tiles, insert spacers to ensure even joints. Drop each tile in place, then give it a slight twist to ensure the thinset adheres at all points. Stand back every few minutes and inspect the joints. Make any adjustments to each section before the mortar starts to set.
Adjust the lines until they are square by moving the chalk line slightly and resnapping the lines. If the diagonal measured more than 5 feet, move the line slightly clockwise with reference to the center point. If it was less than 5 feet, move it counterclockwise.
Measure from the chalked lines a distance equal to an even number of tiles and joints, and snap layout lines at these points in both directions. Use these lines as a layout grid for sections when you lay the tile. Snap additional lines if you need them to help keep your tiles straight.