Wrap a sheet of paper around your grip. So it is tight around your grip. Take a pencil and rub the side of the lead against the paper. This will pick up details from the grip. Then cut it out with scissors and you have your pattern.
Nice decal grips are on Amazon for next to nothing.
My favorite grip mod is the amazon decal grips, covered in designer duct tape. Still get the rough feel, and cool designs. Wal-Mart paint dept.