put a piece of saran wrap under the toilet seat. put vaseline on the toilet seat. put a bucket of water on top of a partially open door. fill someone's car with something (stuffed animals for example). use an acccent and convince someone you are a foreign movie star.
Some good ways to prank people are by calling them as many times on their phone and hang up every time the person tries to answer the call or give fake winning lotto tickets. You can also pretend that you are choking so as to see the reaction of the people or put an ad on your friend's house stating that the house is for sale.
If you can access the physically, take a piece of duct tape. Put a sticker on the inside of the duct tape saying "Lol" on the sticky side, take the piece of duct tape, Attack them by wrapping it around their head. If you're not that good Of friends, take plastic cups. Fill all the cups. Place them down everywhere in their office/desk whatever.