Sayulita's main beach is a crescent of golden sand curving around a bay, walkable end to end in about fifteen minutes. The north end is calmer and better for swimming; the south end catches the surf break and is where the board rental outfits and instructors set up. On weekends the beach gets busy, so arrive early if you want a quieter stretch.
A short walk south of town — or a taxi ride — brings you to Playa de los Muertos, a smaller, wilder beach with no facilities and far fewer people. North of town, Playa de los Muertos and Playa Patzcuaro offer similarly quiet alternatives.
For surfers with more experience, La Lancha (about 8 km south) has better, more powerful waves with considerably less competition.