Measure the height of the wall. Lay a plastic vapor barrier sheet on the floor and cut the length to size. Repeat this process until you have enough sheets to cover the entire wall.
Raise the sheet to the wall. Have two assistants each grab a top corner and raise the sheet to the corner where the ceiling meets the wall. Flatten the sheet out insuring that it covers the entire space from floor to ceiling.
Attach the sheet to the studs. You can use a staple gun or a hammer tacker for this job. Be sure to staple the sheet up and down the studs ever foot or so. This will make for a secure vapor barrier.
Cut off any excess plastic that hangs over the studs with a utility knife. Repeat this process until the entire wall is covered.