Start by measuring your lampshade and determining the size that your circles need to be to fill the entire lampshade. If you want yours to look just like mine, are using the same lampshade and have a Cricut Maker cutting machine, you are in luck!
While your felt circles are cutting, paint your lampshade. I recommend 2 coats to make sure you get really good coverage–you don't want to see brushstrokes when then light is turned on and shines through it.