It may be a result of my upbringing but I've always believed a man should know how to both be put together and show his individual style, one of the simplest ways to stand out is wearing a tie and wearing it well. There are, of course, rules to wearing a tie well.
A tie is never supposed to hang free, but should be secured either by a tie clip secured between the second and third button below the collar or by a vest. Doing both is acceptable but in this case the clip should be worn above the second button, customarilly this is done with clips showing an affiliation, such as a fraternal order, a university, or something of that sort. Regardless of those considerations a tie should be an accent piece, it should contribute to the look of the outfit without stealing attention from the whole. Yes that means no garish designs or too-loud colors. Those are just the very basics.
So, with all those rules, how do you express yourself? Well, first of all wearing a tie and wearing it well tells everyone there you took the time and effort to dress with a bit of sophistication. Secondly, there is the subtle art of the knot. Most men past a certain age know how to tie a windsor or half windsor. They are... basic. Boring. Over the years many more stylish and elaborate knots have come in to the scene and these small details of personal flair can help show a mans own style. Do you go with something thicker and rounder? A tapering arrow? Loose and full, looking like a bloom, or sharp and precise? My personal favorite, a knot that has become something of a signature when I dress up, is the trinity knot.
For more complete instructions videos and diagrams can be found online. There are a lot of excellent resources out there and it never hurts to dress to impress.