How can I get my wall stickers ?

I bought a pack of Nouvelles Images Home Stickers for my wall in my apartment. They are removable and won’t damage walls, that is why I bought them. However, they don’t seem to be sticky enough because they are already falling off. What is an affective way to get these stickers to stay up without ruining my walls? They look so cute and I don’t want to take them down.

Other decals sites

• The Moanin Dove – “Apartment 14″ : The Bay Bridged – San Francisco Bay Area Indie Music
• Car Stickers Are Very EyeCatching Products | Outdoor Table Tennis Tables
• Design*Sponge » Blog Archive » the bouroullec brothers: apartment 50