If you're planning to dance in the streets on Halloween to celebrate the Giants' stunning World Series victory, we recommend you leave your keys at home.
Mass transit is going to be your key into San Francisco Wednesday morning. The route starts at foot of Market Streets next to Justin Herman Plaza. It will move up Market Street, then west to the Civic Center Plaza.
There are three important BART/Muni Metro stations which have exits along the Market Street portion of the parade route:
BART had record ridership on parade day 2010 and plans to use commuter length trains all day long. Here are more tips from BART. BART can take you to the same three stations from all East Bay lines.
The Muni Metro will take you to those stations via basically any of their underground lines -- the J, K, L, M, N or T lines. You’ll need to use these instead of the buses because all surface street traffic will be jammed up, rerouted and confused due to the parade route closures and crowds.

From the Peninsula/South Bay:
Another option from the East Bay or the North Bay is to take a ferry.
From the North Bay:
From the East Bay:
If you will be driving to San Francisco via the Bay Bridge, do not take the 9th Street/Civic Center or 4th Street exits. They will jammed up and you won’t be able to cross Market St. either.
You should opt for the Mission/Duboce exits. You’ll need to find parking, of course, and the Civic Center Garage is the closest to City Hall where the parade ends and the ceremonies take place.
It will likely be packed. You can look for other public parking lots online.
Again, my advice is to park well out of the area and take one of the mass transit options into the area.
With all of that said, getting into the area may be less of an issue than getting OUT of there.
Just like when you go to the movies or a concert, the crowd arrives over time but everyone tries to leave in one big rush. Bring your Clipper card if you have one to speed your access across transit agencies. Bring your patience because with big crowds come big delays. Most importantly bring your Orange and Black and focus on the occasion. Everything’s much easier to deal with when it comes with a side of Championship!
Useful links: 
East Bay Ferries (Alameda/Oakland Ferry and Alameda Harbor Bay Ferry)
San Francisco Parking and Travel Info