By bus
From beach suburbs further north, get on the 155 bus which begins in Mona Vale and goes all the way to Manly.
If you're coming from the city or parts of the lower north shore, jump on any bus headed to the Northern Beaches from Wynyard station such as any number in between 184-190, including L buses, get off at Warringah Mall and then cross the road and switch to a Manly-bound bus the 155 or others. However, if you're in the city, the ferry is by far the quickest and most scenic option. Direct buses to Manly only run during the morning and afternoon peak on weekdays.
From the Lower North Shore, catch the 140 weekdays, PM peak hour only, 143 or 144 bus from St Leonards station or Crows Nest.
By car
From points further north, get on Pittwater Road and stay on it all the way to Manly. At Warringah Mall, Pittwater Road turns to the left which is clearly signposted.
From the City, cross the Harbour Bridge, and take tine Manly exit from the Warringah Expressway, and follow the signs.
Expect considerable congestion during peak times, including weekends. There are a number of parking stations in Manly. Street parking is hard to come by, and impossible to find on a sunny summer weekend.
To beat parking troubles consider carpooling. The owner of the Australian carpool site Jayride (http://www.jayride.com.au...) Based in Manly and markets to the area heavily, so there are almost always carpools available from around Sydney.