Steam to remove window tint
If you have tint on windows and it really baked on over time, use a steamer. I used type for removing wall paper. Worked great and can usually rent one from rental store. Also use very light soapy water mix. If you mix about a tablespoon of dishsoap with quart of water with hand spray bottle. You can chase it off. Takes a little time but a lot safer to window, etc. than razor blade. I have seen windows scratched from use of razor blades. Only use in tough problem areas. Keep a towel under work area as the steam condenses, you will need to keep area below dry.
As for stickers that may not easily steam off, try acetone or finger nail polish remover.