Maybe the ground rules are simply not known, so I'm even bother:
a) dust-free (So off to the bathroom or room 15 minutes before airing), good lighting (desk lamp) at an angle from above.
b roll up, wash) Sleeve hands and dry thoroughly (with a lint-free cloth, better paper towels)
c) dust with a microfiber cloth the surface and especially the edges and make fat-free (but only dry wiping, no liquids), and finally:
d) there is usually only one chance, so sit right on the iPhone, Ca. Deduct 20% of the protector and hold, then and accurately create (on off switch) and quickly remove the rest of the protective films and the actual film to "slide" let. Done.
e) blowing you always get out later, with a little pressure and a cloth (plastic nix) aside rausdrücken.
Have probably already 20 films for 3G / 3GS and now also processes for the iPhone 4, was always top. If the films would not fit, I had noticed that, in that case, I would complain. So my recommendation is the film, even the price.