Lay the ladder flat on the ground with its feet touching the building.
Lift the top of the ladder while pushing its feet against the building. Push the ladder until it rests against the building, enlisting an assistant's help if necessary.
Align your ladder with the proper angle against the building. For example, when your toes are touching the base of the ladder, you should be able to reach out and grasp the rung of the ladder with your arms fully extended. If your arms reach past the ladder, the ladder is not steep enough; if your arms cannot reach the ladder, it is too steep.
Screw a 2-inch by 4-inch cleat to the space behind the ladder's feet. Tie ropes to the ladder legs beneath the lowest rung, and tie the other end of the ropes to an anchored object near the wall, if screwing a cleat to the ground is impossible.
Anchor the top of the ladder into place using a ladder stabilizer.
Check the load designation of your ladder printed on the ladder's leg.