Go outside and survey the damage. Unless the jokesters made a lot of noise while throwing toilet paper all over your house the night before, you won't know how bad the mess is until the morning. Examine where the long lines of paper end and begin, since this can help you minimize the cleanup.
Begin picking up the toilet paper, and place it in large garbage bags. Start with the paper higher up in case some of the smaller pieces fall to the ground. That way you should only clean up the ground once.
Secure a ladder, and grab paper off the roof line or tree branches. This is a good time to ask a family member or friend to hold the ladder steady for you.
Tape duct tape--sticky side out--to a long stick or rake to pull down the paper instead of a ladder. The smaller pieces should stick to the tape.
Remove all the remaining pieces strewn on the ground. This is probably the most tedious part of removing toilet paper. Be patient, and try not to get angry about the situation. Most of the time it's nothing personal, just a good-natured prank.