A great tip to prevent from dripping or spraying sealant on places other than your customer's driveway. Use either a wood board or fiberglass board and have one of the guys helping you hold it right at the edge so you can finish the driveway right up to the wall. This will make for a clean and easy finish to your job.
Make sure to always tip the board towards the waist of the person spraying so that the sealer does not get under the board or on the back of it.
Use the board around the edges and spray 4 to 5 feet away from the edge. You can then finish the main body of the driveway without getting sealer all over the walls or edges.
Hope this helps!