I know for me, the first time I visited Paris, I enjoyed starting at l'Arc de Triomphe (very good view from the top, and an eternal flame beneath the arch, plus it's amazing to watch the chaotic traffic in what must be one of the largest traffic circles anywhere).
From there walk down the Champs Elysée (itself not that interesting) to Avenue Winston Churchill, take a right there and walk past the Grand Palais and the Petit Palais, noting Sir Winston's statue next to the Petit Palais, and then on across the ornate Pont Alexandre III heading toward the golden dome of Invalides with the Eiffel Tower off to your right -- that was a pretty good introduction. If he's interested in things military maybe a quick stop to see the tomb of Napoleon might get his attention. It's pretty amazing.