A nice summary of how to get to UC San Diego can be found at http://blink.ucsd.edu/facilities/transportation/visitor/directions.html.
Flying: UCSD is served by the San Diego International Airport (SAN), 20 miles south of campus; there are also limited charter flight service into Carlsbad (CLD).
The closest station to UCSD on the Amtrak Surfliner line is Solana Beach, from which you can take a taxi or uber, the 101 Breeze bus (which terminates on campus), or your bike (warning: very steep hill up to campus).
For Metrolink, you should transfer to a Coaster train at Oceanside to either Solana Beach or Sorrento Valley stations, and hop a taxi, uber or bike from there. Be sure to check the Metrolink and Coaster schedules before heading down.
Driving: UC San Diego is located in La Jolla, CA, about 15 miles north of downtown San Diego and 20 miles north of the San Diego airport. It is most conveniently accessed from the 5 freeway at either the La Jolla Village Drive or Gilman Drive exits. If you are driving, you are strongly encouraged to carpool to avoid this picture!
Parking is free on weekends, but attendees will have to pay on Friday if they are driving in that night. You can park in lot P103 and purchase a permit (for Friday only) from one of the permit machines in the lot. See http://maps.ucsd.edu for other parking locations.