This is the method I use, I've found it works really well. The shoe polish I use is Kiwi black shoe polish.
1. Wear your boots and place one foot on an elevated surface. (I use one foot on the stairs/chair)
2. Place a small amount of polish on your boot, brush it evenly onto the boot surface
3. Grab a piece of gun cleaning cloth. (The disposable kind, white with red lines) Tear about 4 squares of the cloth, you may keep and reuse this over time.
4. Place the cloth, long side horizontally over the boot and rub it vigorously in a left-and-right motion while pressing the cloth down onto the boot.
5. Repeat with the other boot.