Thoroughly clean the windscreen to remove all dirt, grit and grease. Be careful which product you use to clean the glass, as some will leave a residue behind that will prevent the sticker from adhering well. Most alcohol-based glass cleaners evaporate so will be best for this.
Measure down from each side of the top of the windscreen and apply a little masking tape, to mark the same length at each side of the windscreen. This will help ensure the strip is applied as straight as possible
Remove the backing paper from the sunstrip and apply a thin spray of soapy water to it as well as the top of the windscreen
Apply the sunstrip to screen leaving the excess at the sides and top. The soapy water will allow movement of the strip to ensure it's placed centrally
Squeeze out excess water and air bubbles from under the strip, the side of a credit card is a handy tool for this (one with smooth edges, if in doubt wrapping it in a microfiber should stop it scratching the vinyl). You can pin prick any bubbles that won't go away and press flat if they’re a real pain
Trim off excess vinyl around the glass carefully with a sharp blade
When it is fitted and you are happy, leave it to totally dry before driving off (you don’t want it flying off halfway down the road!)