To make a wand, you'll need 7 stems of lavender, with nice buds or blooms at the top. You can use more stems (9 or 11 or 15, always an odd number), but it's easiest to start with just 7. One set of instructions we found said to let the lavender wilt a bit, but with our sturdy ‘Fat Spike' variety, that didn't seem to make much difference. You'll also need a length of narrow ribbon (we used ¼ inch satin ribbon, probably at least 3 feet, although I didn't measure since we just used it from the spool).
Gather the stems together, and tie one end of the ribbon just below the lowest flower buds. You can leave a shorter (3-4 inch) end to just tuck into the end of your wand with the flowers, or you can leave a longer end (12-15 inches) to use in making a bow at the end. For your first wand, cut the end shorter, so it doesn't get tangled in your stems as you weave.
Now you start bending the stems down over your ribbon knot, down toward the blooms. Try to arrange them as symmetrically as possible. It'll start out looking like a strange, stiff-legged octopus, and then when you gather the bent-over stems in your hand you'll see that you've enclosed the blooms in a "cage" of stems. You're going to weave the ribbon in and out of the bars of this "cage" to further enclose the flowers. Not only does the ribbon make the wand look pretty, but as the lavender blooms dry the ribbon will keep them from scattering all over the place.
The weaving is simple, but it takes a little time and patience, especially with the first row or two until you work out a system. Gently lifting a stem from the bundle allows you to slip the ribbon under it, then the ribbon goes over the next stem, under the one after that, and so on. The rows of ribbon alternate, so that if the ribbon went over the stem the last time, it will go under the stem on the next row. Try to keep your stems spaced out fairly evenly, and try to keep your ribbon rows somewhat horizontal. As you go along, you can tuck in any lavender buds and flowers that try to escape, as well as tucking in that short end of the ribbon.
When you get to the end of the flower buds, you could simply secure the ribbon with a knot around the stems and then add a ribbon bow. We wanted a finished look for our "magic wands," so we wrapped the ribbon in a tight spiral down the stems to the bottom. Then we reversed the direction of our spiral and went back up, securing it with a knot at the base of the woven section. A butterfly decoration provided the perfect final touch!
Once you've got the basics down, you can try wands with more stems and can experiment with different ribbons and weaving patterns. Our first wands had a more rustic look, and our later attempts were more polished in appearance.
But remember, this isn't meant to be a precise craft. With botanicals, a handmade look is part of the charm. In the end, your goal is to enclose most of the lavender buds and blooms inside a wand-shaped cage of stems and ribbons. The tightness and precision of the wand's shape is really not important. I asked my niece what advice she would give to somebody making their first lavender wand, and she said, "The first one you make is probably not going to come out perfect." And that's OK.
 I'm referring of course to the stunningly popular series of books by J.K. Rowling, published in the US by Scholastic Press beginning in 1988.
 We read several sets of directions online when we were looking for information. This is the one we found most useful: Lavender Wands and Lavender Bottles. Thanks, Jane Lake!