Take the I-5 north to exit 27, Gilman Dr., and follow Gilman Dr. up to campus. Once you secure parking on campus, proceed to Mayer Hall, 4th floor. 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.
A map of parking locations on campus can be found here. Parking is by meter or by permit. Please let us know in advance if you would like us to get a visitor permit for you, which we can buy at a discounted rate. Your permit will be available for pickup at Village 15 when you arrive. Otherwise, you can buy a V permit at the nearest pay station for $2/hour or $20/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.