When you are in Geneva and you have got enough time, go to Annecy.
In Annecy you can find sth for anyone. Visit the beautiful city-center, old town, stroll along the lake or river, go shopping, visit "petite boutiques", go shopping, have an ice-cream/coffee/crêpe somewhere.
Caution: Extremly crowded on Saturdays!
Check online or the train station for timetable. I would recomment though to take the bus from/to Eaux-Vives, because it was a scheduled 2h-trip, but depends on the traffic. On our way back we took that one and arrived in Geneva only a hour later.
Round-trip was 33 CHF.
Take the boat excursion
on the Lake Annecy
and see the alpine mountains on a surprising angle!