You can walk, drive or bicycle across the bridge with more information here. But the best way to get up close and take pictures is the Blue & Gold Fleet Bay Cruise, or a Ferry to Sausalito located at Fisherman's Wharf.  One is a general cruise around the bay under the Golden Gate Bridge and around Alcatraz for great pictures.  The second is a ferry boat that goes to Sausalito, a scenic waterfront town across the bay.  Do some window shopping and have lunch at the Trident Restaurant along the waterfront, then return on the ferry to San Francisco.