After entering the park, keep driving the loop until you get onto Northside Drive, and then park once you are right below El Capitan (the 3,000ft granite monolith that is very hard to miss).

Once you've parked, grab a blanket, snacks, and a beverage.  With these items in hand, walk over to the eastern side of the meadow and stay on the designated path that goes past the fences and into the meadow.  Now  find a spot to relax and enjoy the sunset.  A spot that is my personal favorite is right next to the tree on the eastern side of the meadow.