Select the proper dowel. A dowel makes a hardy staff for your scepter. Consider the size of the person who will wield it -- a small, thin scepter will not look regal enough for a large king, for example -- and choose a complimentary length and width.
Decorate the scepter. If you do not feel up to carving your dowel, draw a pattern on the wood to simulate carving and cover the drawn lines with a steady, uniform stream of hot glue. When the glue dries, it will add a carved-esque third dimension to your scepter's shaft that makes it look more real.
Paint the scepter. Depending on what precious metal the crown is supposed to be and the color palette of the monarch's costume, paint your scepter gold or silver. Spray paint will cover the scepter evenly and dry quicker than brushed on paint.
Accessorize the staff. Use the hot glue gun to affix fake jewels to the painted dowel. Different colors will pick up and reflect different stage light colors, so select a variety of glass gems for your scepter.
Top the dowel. Most scepters have an open rounded object on the tip. You can use just about anything for the tip base -- a wooden or plastic ball, a ball of grapevine from your local craft store, a flat disk, or a flat crown shape you've cut from particle board or a sheet of 1/4-inch thick plastic. Decorate the tip to match the dowel with hot glue, paint and jewels.
Go for the laughs. Gold paint and glass jewels are fine for serious kings and queens, but a royal fool or Lord of Misrule needs something far less fancy. A plain dowel with a toilet tank floater screwed to the end of it makes a great foolish scepter, as does a stick with an inflated pig bladder dangling from a string tied to one end. An unadorned bathroom plunger will work, too.