We lay flagstone patios in stone dust, not cement.
Before placing the stone, we spread a 2-inch-base of stone dust and tamp the surface smooth. Then we place and level each piece of stone. We deliberately allow 1/2-inch or 1-inch veins between stones since each piece is not cut to exact measure. Thus, veins allow for unforgiving stone cuts. Stones are laid in a checkerboard pattern so seams are staggered.
For aesthetics, we alternate a 2-foot by 3-foot piece with a 2-foot by 2-foot piece. Each piece is between 1 and 2 inches thick. The thicker the stone, the more stability it offers. When the patio is in place and level, we sweep more stone dust on top of the floor so the it settles into the veins. The face of the stone is etched to provide “relief”—a far more natural look than a manufactured piece which is perfectly smooth.
For stability around the perimeter, we use wood or hard plastic/metal. The wood collar comes in two sizes (4-inch by 4-inch or a 6-inch by 6-inch and is pressure-treated pine). The hard plastic/metal is 1/8-inch thick and sits against the side of the stone. It has "legs" which are driven into the ground for stability.
We water the stone patio to clear the film of dust off each stone's face. Water also tends to harden the stone dust in the veins. You may walk on the patio immediately after it is laid.