You could easily spend a week in La Jolla, walking on the beach, puttering around town and enjoying meals in great restaurants; but if you only have one day, you can still enjoy some of the best La Jolla has to offer.
You'll want to start off by going to the beach. La Jolla Shores is one of the best beaches in the state of California, with a gently sloping beach and panoramic views. A sunset or morning walk on the beach is enough to relax even the most stressed individual. The walk is better with the tide going out, as it leaves the beach with a mirror like water display.
La Jolla is home to some of the best restaurants, with many of them serving excellent cuisine at lunch, although a lower price at night. This way, you can live large on just the right budget.
Something else you'll want to do is go tide pooling. The Tiny La Jolla Cove is a couple of blocks away from downtown, and accessible by a stairway. At low tides, the tide pools will have hundreds and hundreds of hermit crabs.
Walking around is also a great way to spend part of your day. You can go for a window shopping stroll along Prospect Avenue and the side streets there. With chain stores in sight, you'll probably find something you must have.
If you have time to stay through the evening, the La Jolla Playhouse is worth your time, as it offers plenty of entertainment for the entire family.
For just a day to spend in La Jolla, there is a lot that you can do. Once you spend a day in La Jolla, you'll probably find yourself wanting to come back for more - the town is simply that good.