LA Backwards Beekeepers Kacy and Bethan made this great pictorial series about how to make wax starter strips for your frames.
# I: First Kacy wets down a piece of 1 x 2 pine that's cut or marked to the length of the frame.
#2: The melted beeswax is painted onto the wet board with a chip brush. 2 or 3 coats will do it.
#3: Bethan cuts the strip down the center of the board with a razor blade, so two strips, about one inch wide apiece, are made.
#4: Using a cake spatula, the wax is scraped off the board. It comes off easily since it's wet. The board is rewet and wax repainted on each time.
#5: The strips are placed in the slot at the top of the frame.
#6: Popsicle sticks are pushed into the slot alongside the wax. It takes about 3 3/4 sticks per frame.
#7: Hot wax is then painted over the popsicle sticks and the base of the wax to cement them into place. Try not to get too much wax on the existing strips or they'll melt down.
Here's a video showing another method of making starter strips (which includes an explanation of what they are).