There are several reasons that a porch or deck might require propping for repairs. In most cases, it is due to the support posts settling into the ground. To correct the issue, you must prop the deck up to a level position so you can place additional dirt or cement under the supports or so you can replace the supports altogether. The process of jacking up a porch or deck is not much more difficult than jacking up a car.
Remove any obstructions that prohibit access to the framing of the porch in the area where the porch is closest to the ground. This includes lattice and landscaping. In most cases basic tools like a screwdriver work to remove lattice.
Place a piece of 1-inch-thick plywood under the front edge of the porch. Position it in the middle of the front joist. The joist is the large beam that all of the floorboards secure to on the front of the porch. Ideally the plywood should measure at least 12 inches by 12 inches to prevent the wood from sinking into the ground.
Place a level on the front of the deck so one end faces the house and the other faces the end of the deck you want to jack up. Use the longest level you have.
Place a scissor jack between the plywood and the porch's front joist.
Jack up the scissor jack until the level on the porch indicates that it is level.