The best approach I have found is to make sure that you position your head and mouth so that the angel of the other guy's cock moves smoothly down your throat. Most guys cock natually bend downward, so allow your throat to open in the direction his cock is bending. Another observation that diminishes the gag reflex is to breath out as his cock slides into your mouth and throat. Following this practice of breathing out as you go down on the other guy will allow you to take the longest cock to his balls. Let me know if this works for you!