Get on to I-10 follow it west to Los Angeles. Continue following I-10 which will be signed To Santa Monica. You will need to take a 1 mile dogleg on the I-5 but following the signs to Santa Monica will get to the I-10 which you continue heading west on. When you get to Santa Monica, continue west and go thru the tunnels at the end. When you exit the tunnels you are then on Pacific Coast Highway (CA-1). Follow that North and then west, for about 4 miles or so and you will be in the city of Malibu.
In short get on I-!0 in Texas and follow it west until you go thru a tunnel and end up staring at the Pacific Ocean.
Legs? Can't say but try to arrive at downtown LA between 10am and 3pm weekdays or on Saturday or Sunday. The route takes you straight thru the middle of the traffic knot of downtown LA. There are no alternate routes, don't even try to look. I-10 west is the best of a bad lot.