Start at the Place de l'Etoile (officially Place Charles-de-Gaulle, but nobody calls it that), preferably at the top of Napoleon's gigantic Arc de Triomphe, from which you'll get a good view of the 12-pointed star formed by the avenues radiating from the arch in a tour de force of geometric planning.
Place Charles-de-Gaulle is its official name, but everybody calls it Place de l'etoile.