Before you lay any bricks, plan your patio layout. If the slab is the same size as a multiple of whole bricks (including mortar joints) lay the border first, then start setting the brick at the border, as shown on these pages. If the slab has control joints, start along the joints and work toward the edges.
Joint width depends on the relation of the brick's actual size to its nominal size. Generally if the actual size of a brick is 1/2 inch shorter than its nominal size, you'll make 1/2-inch joints. If it's shorter by 3/8 inch, you'll space the bricks at 3/8 inch. You can adjust spacing for aesthetics. Cut plywood of the desired thickness for spacers.
If you're mortaring your borders to the surface of the slab instead of setting them on the side of the patio, build forms to contain them. On a new slab, remove the slab forms and reset them 1/2 inch higher than the surface. This small edge will keep the border material in place. For an existing slab, dig a trench around the slab and install new forms.