While it's easy to just buy a broom, it's also pretty easy to make one of your own out of different types of wood. Although the items that follow are for the more traditional style of besom, you can use nearly any types of branches available to you. You'll need:
A four-foot length of ash or oak for the handle
Thin branches of birch for the bristle part (you can substitute a woody herb like mugwort or thyme for the bristles if you like)
Lengths of willow or heavy cord to bind everything together
You'll also need scissors and a bucket of warm water. Whatever you'll be using for the bristles -- whether it's birch, an herb, or some other wood -- should be soaked in the warm water overnight to make them pliable, as should the willow binding, if you're using it.
Line up your broom handle and bristles, with the bottoms of the bristles pointing towards the top of the handle.
Lay the handle on a table or the floor, and place the bristles alongside it, lined up about four inches from the bottom. Point the bottom of the bristles towards the top of the broom, because you're going to flip the bristles in a minute (see Fig. 1).
Tie the bristles in place around the handle.
Use the willow branches or cording to wrap the bristles around the broom (Fig. 2). Add as many as you want to make the broom full. Make sure you tie the cording off securely so your bristles don't come popping out later.
Finally, fold the bristles down over the inner tie, and then tie on the outside.
Now, take the bristles and fold them down over the willow binding or cording so that they're pointing towards the bottom of the broom. Tie them down again at the base of the broomstick to secure them(Fig. 3). As you're wrapping the cord in place, visualize your intent for this besom. Will it be strictly decorative? Are you going to hang it in place over a door? Perhaps you'll use it ceremonially, or maybe even for physical cleaning. Focus on what you're going to be doing it, and charge it with energy.