The Handyman's Guide to Concreting at Home
Hammer some wooden pegs into the ground to mark out the area you want to concrete. Use wooden pegs about 25mm square, and long enough to be rigid when driven into the ground. Then stretch a strong string, or twine, between the pegs. You can cut your pegs off a length of timber.

Next, decide how high you want the concrete in relation to the ground around it. Remove turf or loose soil from the marked-out area. If the ground is soft spread sand or ashes over it to make a better base. You may have to fill holes in the ground with stones, broken bricks or any clean fill. Final levelling is best done with sand after you’ve put in your formwork. When the whole area is flat, compact it by rolling, walking or driving over it, and hosing it lightly. The more it settles the better the foundation for the concrete.
DIY Alsafe Concrete