If you have a more mature guinea pig, teaching paws up is a great way to improve balance, which can help when teaching some other more advanced tricks. For example, many middle aged, older, or overweight guinea pigs are hesitant to stand up on their hind legs, or lift their front paws off the ground at all. Learning to put their paws up on an object gets them comfortable with their paws being off the ground, while still having the safety of something to lean on.
For the written step by step tutorial and photos, visit the How to Teach a Guinea Pig: Paws Up page.