From the UK:
There are direct cheap flights to Los Angeles from most major UK airports, landing at Los Angeles International Airport (LAX), 15 miles (24km) south-west of the city. The flight duration from London to California is about 10 or 11 hours, depending on destination.
Don't assume that all international flights leave from the international terminal. Many don't, and some carriers even operate some of their international flights from there and some from other terminals. Its is always important to check the terminal for international flights carefully.
There are also two executive terminals for charter aircraft if time means money.
In LA, an automobile is nearly essential, and connections to and from the airport are poor. There is no direct train service, although there are free shuttle buses to Aviation Station on the Metro Green Line, and half-hourly LAX FlyAway shuttles to Union Station ($7.00 one way). Taxis to downtown L.A. cost $45.00 and take 30 min in good traffic but can be far slower in rush hour. On your return to the airport, be sure to arrive 2 h before your flight as queues for security are notoriously long and often time-consuming.