Book online for timed entry, or skip the summit and ride only to the 2nd floor (cheaper, faster). Or just admire from Trocadéro.
The Trocadéro plaza across the river offers the classic Eiffel postcard view. Free, always open, photogenic at sunset and during the 9 PM sparkle.
The tower sparkles for 5 minutes every hour on the hour after sunset. Plan to be at Trocadéro at 21:00 in summer (later when daylight savings ends).