Peel off as much of the sticker as possible with your fingernail or a plastic scraper
Soak the sticker with warm soapy water or glass cleaner
Let it sit for a few minutes to loosen the adhesive
Use a plastic razor blade or credit card to lift the remaining sticker
Apply rubbing alcohol, vinegar, or adhesive remover to the residue
Wipe the area with a microfiber cloth
Repeat soaking and scraping if needed
Clean the window with glass cleaner after the sticker is removed
Avoid using metal blades that can scratch the glass
Use a hair dryer on low heat for stubborn stickers before peeling