Originally Posted by Manton
To make a decent dimple, I find it works best to tie the tie loosely, as noted above. Don't cinch the knot tight and then pull it up into the collar. When you put the front blade through to form the knot, leave it loose. Make sure the part of the front blade that is inside the knot is spread out and smooth, without any folds. If you pull up the knot and there are already folds in there, they will set and make a centered dimple impossible.
Gently pull the knot up into the collar before you tighten it. Then work in the dimple as you tighten and fix in place the knot. Basically, all you need to do is press an impression into the tie, just below the knot, with your index finger. Make sure to center the impression. Then, as you gently tighten the knot, keep your index finger there and use your thumb and middle finger to hold the sides of the dimple even. Don't over tighten. If your knot ends up looking like something worn by the cast of LA Law, it's too tight.
+1...It's really simple just try it a couple of times. Pinch the tie between with your index finger between your thumb and middle finger before you tighten the knot. Hold the pinch as you tighten and move the knot up to your collar.