And here it is your answer: the tip should touch the top of your belt. Have a look at the picture. The tip should never go longer than this. It could be a little shorter but never to the point of showing some shirt between the tie and the belt.
If you are not wearing any belt, just imagine where the belt would go or just don’t leave any shirt showing between the tie and the pants. Got it?
And if by any chance you want to break this rule, go shorter (but just a little bit, showing an inch or two of the shirt), never longer. Deal?
I don’t know if you know but tying a tie in a classical way requires a dimple under the knot. Do you? It does. Besides that, tying your tie with a dimple will give a certain personality to it and will make the knot smoother therefore will drive more attention to your face. Because when there is no dimple it is like you focus there, on the knot. It screams for your attention. When there is a dimple, it gets softer and your attention is no longer demanded there. Just compare.
And yes, a dimple is this indentation, this little fold under the knot.
If you don’t know how to actually give your tie a dimple, here it is the way I learned:
Just tie your tie the way you normally do it until you are going to finally tie the knot tight.
Then before you pull the tie to make it tight you put your index finger just below the knot and pinch the tie in a W.
Then pull the tie from the loop til the knot is tight as you like.
In the video below you can see this way and another way to give your tie a dimple.
Either way, just don’t forget about the dimple. And yes, you can keep on tying your tie without the dimple. Or alternate between the two options (with and without). Let your own style (and mood?) decides on that.