I was recently asked by a customer what the correct and proper length of a tie should be.
So I whipped up this sketch.
For most people, especially for those in professional services, the tie should end somewhere between the top and bottom of your belt buckle. This universal rule ensures you look proportioned and professional.
A tie too short automatically makes you look more rotund with a large stomach. A tie too long makes you look a bit daggy - not in a good way.
Between the choice over too short or too long, I'd choose too long everytime. Also, some of the men known for their suiting prowess (e.g. George Clooney, Brad Pitt), have been known to keep their ties a little longer. As fashions change, so will the length. If you're feeling real daring, you could even keep the tie a bit long and tuck it in. This is the edge of fashion though, so be prepared to wear it proudly!
The broad part of the tie should always cover the narrow end (which they're designed to do). If you really can't get it to work, you can often slip the narrow part of the tie through to the inside of your shirt so it doesn't stick out below. In the long term, I'd get my tailor to shorten the narrow end ever so slightly so it can sit naturally and not show up.