Choose between the two routes which combine train and bus service from Union Station to San Francisco. Pick the inland route only if you want to spend most of your time on the bus, but the Pacific Surfliner route is better--it travels from Los Angeles to Santa Barbara and then offers bus service into San Francisco.
Call Amtrak at 1-800-USA-RAIL or visit Amtrak's web site in the "Resources" section below. On the web site, you can book your train reservations via Amtrak's Fare Finder. You can also navigate the site if you have a PDA, Blackberry or other handheld device.
If you ordered your tickets online or by phone, pick them up at a ticket agent or at one of the Quik-Trak kiosks that can be found at many Amtrak locations (you'll need to enter your reservation number). If you've booked your trip far in advance, you can also request that your tickets be mailed to you.