Upon starting, head right. You'll encounter your first Goombas. Use Jump stickers to defeat them. Continue right, peeling any visible stickers from the environment. You'll find a Toad who explains the basics of peeling. Further along, you'll encounter a block with a Super Mushroom sticker. Always keep a few healing stickers handy!
Proceed to the right, jumping over gaps and hitting any question mark blocks you see. You'll eventually reach the end of the stage and the exit pipe. Before leaving, ensure you've collected a good variety of basic Jump and Hammer stickers. These will be your bread and butter for early encounters.