In NJ and PA, there can be no tint on the windshield or front side windows, only on the other windows. Each state will have different laws.
I tinted the windows in my old 1983 Malibu wagon in the mid 1990s. It was easiest when I took the windows out of the door and removed the hatch, and tinted them on a table. The large rear side windows were more difficult. Use lots of soapy water. Don't use a hard plastic squeegee or it will leave scratches (my experience). Use something like a silicone squeegee with more soapy water on the squeegee side of the tint.
Don't use ammonia-based cleaners on the tint or it will change the tint to an odd reddish color. That was the effect in the 1980s and was seen in lots of cars in Florida when I lived there; I don't know if tint has been reformulated since then.