Simply put, Trocadero is where you have to go to get the best views of the Eiffel Tower.
When you’re heading out of the Metro, use the “Tour Eiffel” exit. You’ll arrive in an open space full of tourists and souvenir vendors. As you wander among the crowd, you’ll pass by the Palais de Chaillot (there are various museums there) and see the Tower on the other side of the river. Once you cross the river, you’ll arrive at the Champs de Mars, a favorite park for picnics in Paris.