Mark the start point of the groove with the lumber pencil (using your tape measure to locate this point).
Mark the next point (the same way you did in step 1), and move on to any other points in the groove (if the groove is to have more than one straight line).
Stretch the chalk line from the first point you made to the next (the end of the chalk line string will have a cleat that will grab the edge of the concrete, or you can have another person hold it to the ground), while pulling the string tight over the concrete surface.
Pull the string about an inch from the concrete surface and release; the string will snap to the concrete, creating a thin, straight chalk mark that will guide your groove cut. Repeat this step for any remaining groove lines.
Set the diamond blade to the desired groove depth, and turn on the water hose to a small trickle.
Turn on the saw and gently ease the blade to the chalk mark; once the blade is completely cutting in the concrete, slowly push the saw along the chalk line while applying small amounts of water to minimize dust and aide the cutting. Continue this until you have reached the end of the chalk line and move on to the next.
Cutting Wide Grooves
Chalk secondary marks parallel to the original marks at the width you need.
Cut these lines as you did in step 6 above.
Begin chipping away the concrete between the cut lines using your electric hammer, and continue until you have a hollow groove.