I recently bought a proper 'not tied for you in the factory' bow tie. Just a strip of wavy fabric to be assembled about my own neck! I figured I'd look (even more) dashing with the genuine article, tied just imperfectly enough to make it clear that it's the real deal. The instructions on the back of the box were frankly useless so I turned to Google and after a few pictorial, textual and video tutorials I got the hang of it:
It's not easy, and definitely requires a decent understanding of what you're supposed to do, then some practise until you can actually do it, followed by more practice to fettle it into looking half decent. It's worth being familiar enough with the procedure to be able to replicate it as necessary, since you may find some joker pulling yours undone at the ball! But my friends would never do that. And I had a backup pre-tied one in my pocket just in case.
My Marks and Sparks version came with an adjustable clasp in the middle, which is very useful to fit it to the neck properly and allows your hard fought bow creation to be saved for next time.
So, where are my instructions on how to do it? I shall cheekily defer to those that have gone before me, but humbly suggest that the easiest to follow description, and certainly the one that really sorted me out, can be found here: http://www.youtube.com/watch?v=VJv4Qh7zR3E
Of course the very best thing about a real bow tie is that you can do the 'just heading back to the yacht in Monaco harbour for a night cap' look: