"Rules" for Lampshade Selection

Firstly, the simpler the body shape of a lamp, the more varied styles of shades it can take.
You can repeat the shape of the lamp body in the shade shape. For example, a round lamp on a square base can take a shade with a round top and square bottom.
Generally, the diameter of the bottom of the shade shouldn't be greater than the height of the lamp body (to the bottom of the socket).
Match lampshade colors to the trim color of your room and the tones in the lamp body. Boldly use black or color as an accent if you prefer, no afraid.
Consider the wattage needed! The lampshade instead of lamp body determines the maximum wattage.
Think of the lamp style when selecting a shade. A busy lamp usually calls for a plainer shade.
If you want something special, then break the rules! Try "extreme" shades! Put a deep cone shade on a short round ball base, a glossy white shade on a beige stone vase, a cube shade on a stacked ball lamp, a red or black shade on an Oriental base, etc. The dramatic effect will be definitely breathtaking.