Patios typically are placed outside of an exterior door to allow easy access. Consider sunlight patterns when placing the patio to try to maximize, or minimize, the sun exposure. Also consider what you plan to do on the patio and the type of furniture you plan on using to allow for sufficient space.
The last thing to consider is drainage. Design the patio to shed water to a place where it will not pool in the yard or cause erosion. One strategy is to shed the water into a shrub or flower bed along part of the perimeter of the patio.
Also consider how you will get rid of the soil that will be excavated in order to place the patio. Many yards have depressions or holes that could use some fill dirt or berms that could stand some extra dirt as well. Another good use for it is to place it against the foundation and slope it away from the house to improve drainage of rain water. Just make sure to compact it with a machine or by hand.
Once you excavate the patio area and pass a compactor over it, you will need to bring in crushed stone to fill it and provide a solid base for the patio. Think about access to the patio area. Can you get a truck nearby or will you need to stage the crushed stone somewhere else and transport it in wheelbarrows to the site? In that case, cover a portion of the driveway with plastic and stage the stone there to prevent damage to your lawn.
The same question holds true with the cement truck. Can it approach the patio or will you need to haul it in wheelbarrows? Check to see if your neighbors have access in their yards that would allow the truck to get closer to the patio area. While it is possible to hand-mix the concrete, it is a good idea to use a concrete truck for anything but the smallest of patios, as hand mixing can take several days for larger patios.
In order to pour the concrete, you will have to make a form to pour it in. To make sure that form is level, use a level and draw a line on the house to mark the top of the patio. Set a straight board on both sides of the patio area, with one end butting the wall. Use a framing square to make sure the boards are at a right angle to the house.
Line up the top of the board with the level line, and then place a level on top of the side board. Raise or lower it until the board is level. For every foot the patio extends from the wall, it should drop 1/4-inch for drainage. Measure out from the wall until you reach the desired length. Now multiply the length by 1/4 of an inch and measure down from the top side of the board to determine where the end of the patio will be. Run a form board between the two boards to set the height of the outside edge of the patio, and then install two side form boards that run from the wall to the outside edge. These form boards go in place of the boards used to determine the slope of the patio.
For long patios, run an extra form board in the middle of the patio from the wall to the outside edge. It is important to use straight boards for the form because you will place a board, known as a screed, on top of two form boards and pull it back and forth to level the top of the concrete. This middle form board sometimes is needed on longer patios where the screed won't reach from one side to the other. The screed doesn't have to be anything fancy, either. A straight two-by-four will do.
To hold the form boards in place, drive stakes into the ground on the outside of the boards and screw them to the form. You can find the stakes ready-made in most home improvement stores. Screw from the outside of the form so the heads will be accessible after the concrete is poured. It is a good idea to squirt a dab of caulk on each screw head to keep concrete from hardening it. Caulk can be easily removed later when it is time to remove the screws.
Have extra help on hand, and make sure to lock your pets indoors to keep them from interfering. If you are using a wheelbarrow to deliver the concrete, make sure to have at least two. This will cut in half the time needed to haul the concrete, and if one becomes unusable, you can still continue working.
Place wire reinforcement in the patio area before pouring the concrete. Once the concrete is being poured, yank on the wire to lift it off of the ground about an inch or so. You don't want it protruding from the surface, so don't pull up it too far.
Gently wet the surface of the concrete every two hours for two to three days. This will help the concrete cure strongly and crack free.
Remove the form boards once the concrete has cured for a week or longer to help prevent broken edges or corners. Bang on the outside of the form boards with a hammer to help separate them from the concrete before removing them.