I tinted my windows ten years ago with excellent results with a DIY kit from ebay. The key is to wet the window with soapy water first and then get a sharp blade and scrape your windows as there are loads of little bits stuck to them that you can't see. as soon as you start sliding the blade down, you'll feel it hitting the little bits which would ruin your tints. Once you've done that, squirt more soapy water over them and apply your tint. Slide it around to your desired position and then start to squeeze out the air bubbles with a credit card and don't forget to tuck it down behind the door card. As mentioned above, it's better to remove it to make sure of a good job. Once it's all in position, cut it to shape. Job done!