The best beaches in Bali are found in the south: around Kuta, Jimbaran, and the Bukit Peninsula. Some of these are also very busy, of course (particularly Kuta). Hop on a bus or rent a car and you can find some great stretches of sand with few other tourists around. Bali is a year round destination so concern about weather and seasons should be put to rest. That said, the best weather on Bali is usually found from April to September.