Some ties will have neck sizes marked on the loop. If so, place the hook one number up from the number corresponding to your neck-size. This will give you a little larger loop, but will simplify the beginners efforts at tying the darn thing. Button your collar at the neck, then fold it up so that you can slip the tie easily around your neck. This helps you tie it in the right spot the first time, and also helps prevent wrinkling and stretching the tie fabric.
Bowties are generally narrow in the middle and widen out to an hourglass shape on both ends.
The narrow curves are where the knot will be tied. The wider places form the loops and ends of the bow. Put the bowtie around your neck, seams to the inside. The other side should be an inch or two longer. Hold the spot just above the widening point with your nondominant hand between thumb and forefinger.