I have trouble working out all three values of colours simultaneously (hue, saturation, lightness), so I render in black and white so I can focus purely on lightness, then I choose the hues and compose the colour theory, then I use saturation to finalise the composition. I just can't do all three at once because I don't do it enough. Other people can do all three at once. You might find it easier to start with hues, then saturation, then lightness, or do say, hue and lightness together, then saturation. You'll find your own way in time, you just have to keep playing around.