Take the I-5 north to exit 29, Genesee Ave and turn left. At the top of the hill, turn left at North Torrey Pines Road. At the first light, turn left on Northpoint Drive into the UC San Diego campus. Follow Northpoint Drive past the campus Information Booth. Continue on Northpoint as it turns right and becomes Hopkins Drive. Turn right on Voigt Drive. Enter the Hopkins Parking Structure at the top of the hill (Level 6). Super Shuttle is very convenient and costs about $30 plus tip one way to UCSD. Rideshare options are also convenient, and also cost about $30.
Uber or Lyft are very effective around campus, and are the best way to get from the airport to campus. Note that there are specific places at the airport to catch these services, they're called out in the app and they are well-signed at the airport
See http://www.sdmts.com/ for public transit info.
The nearest parking is the Hopkins parking structure. A map of the Hopkins parking structure and other parking locations on campus can be found here. Parking is by meter or by permit. You can buy a V permit at the nearest pay station for $3/hour or $30/day. They are valid in the V,S, and most of the B zones—see here for more details.
Anyone who has a permit from another UC campus can use their permit to park here, but will need to stop by the parking office to receive the reciprocal permit for UCSD. Note that off-campus parking that is walking distance from Mayer Hall is not reliably available.