Make sure you review some of the ladder safety and scissor lift safety information on YouTube before you attempt to work at heights. Many people have been pinned against an object as a result of tipping a scissor lift and some have died from suffocation as a result.
Use stand-offs and tie-offs for the ladder as necessary and leg levelers as required. Also observe the proper angle for safety, which is about 4 to 1 or 75 degrees and never more than 3 to 1 or 66 degrees. Use stakes or boards to secure the feet and don't climb above the third rung from the top.