Start at metro 8 Invalides and take a quick look at the surrounding monuments including “Les Invalides”.
Cross the Bridge “Pont Alexandre 3”, walk towards the Champs-Elysés (the Grand Palais and Petit Palais will be respectively on your left and right).
Once on the Champ-Elysées, walk up the avenue. You may consider meandering in few streets on the side of the main avenue to get a drink or a coffee (Rue de la Boétie / Ponthieu / Berri) offer some decent café if you want to experience this area.
On Les Champs, LaDurée is famous for its macarons and could be a nice (but expensive) stop.
Once at the, you may consider paying a quick visit for the view from the top of “Place de l’Etoile” (the meaning of Etoile should appear obvious once up there).
Then you can get Metro 6 from Charles de Gaule Etoile which will get you in no time to the Eiffel Tower. I wouldn’t bother walking up, it’s crowed and time consuming.