Trying to adjust a necktie without a mirror is difficult. If you're tying it for someone else, it's near impossible. Crazy Russian Hacker has a few quick steps to prep a tie on a table for anyone, without a mirror.
The secret here is a bit of coordination and rope tying skills. Place the tie on a table, then create the knots and just pull them through. It took me a few times to get the hang of it, but it works. The major downside is it only works with one style of knot -- but it still looks great in a pinch. Check out the video for the full details on this tie shortcut.
How to Tie a Tie Like a Ninja [Crazy Russian Hacker]