Study math; when mathematicians point letters to things, they typically do it alphabetically. For instance, if we're naming functions, the first is f, the second is g, the third is h. Vectors go u, v, w, and variables go x, y, z. I'm sure there's other triples that just aren't springing to mind.

Anyway, I use triples for fine-tuning and a general sense to know the letters typically used for functions come after the letters typically used for constants, but before the letters typically used for vectors.