My Very Easy Method: Just Set Up Nine Planets
The first letter of each planet's name, in increasing distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto.

CHNOPS
From this alternate spelling of a favorite liqueur, the six elemental building blocks of life: carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur.

Roy G. Biv
The name of this nonexistent person holds the first letter of each color in the visible spectrum, in order: red, orange, yellow, green, blue, indigo, violet.

Oh, Be a Fine Girl, Kiss Me!
The first letters of these words provide the stellar classifications, from ultrahot O stars to cool M stars. More PC version: Oh, Be a Fine Guy, Kiss Me! Better yet: Only Boys Accepting Feminism Get Kissed Meaningfully.