To all those guys out there who can manage autofellatio, and some who can't, I have three words for you: yoga, yoga, and yoga. I personally have always had the length and some of the flexibility required for autofellatio, although for some days afterward I'd always end up with a sore neck. Just recently I started doing yoga exercises, and most of my problems have disappeared. Not only do I lose the sore neck, but I can also go farther (helpful for those who can't quite reach), even ending up about a half-inch onto the shaft or so! Yoga is an effective way to stretch your muscles (making injury less likely) and greatly increase your flexibility. And, finally, all guys who claim that it's gross only say so because they can't. Trust me, if they could, they would!
[Note: Overeager autofellatio attempts can be dangerous to your neck and back. If you do attempt it, proceed slowly and cautiously – and remember, most guys are simply physically incapable of achieving this technique.]