How much white or black is added (tint, tone, shade)
What colour harmony are you using (analgous, complementary, monochromatic)
Where is the colour on the colour wheel (primary, secondary, tertiary)
What if there is no colour (neutrals)
What is the colour temperature (warm colours, cool colours)
What are the basic categories of colour (hue, saturation, value)
Ok, I know this is Sesame Street, but if you watch this through two times you will never forget which are primary and secondary. You will also remember how to mix the primaries from 2 secondary colours.
Try what professional artists and designers do when trying to find colours that look great together. Check out the Adobe Colour page. It lets you experiment with harmonies, value, and hue.