I also used to struggle with the lights and darks, a.k.a. values. Ignore colour for now. Colour comes last. Practice with drawing, as it is the foundation which will teach you the control of your values (light vs dark). You have to train your eye to see the overall image and not be lost in the details of either light or dark.

• The darkest lights, should never be darker than the lightest darks.
• Squint or if you wear glasses, take them off, to see the overall division of light and dark.
• With the drawing (or painting) start with an initial value statement - start the image with only a binary representation of light and dark, no shading in the lights or darks, leave the lights white and fill all of the darks in as one unified block of a middle shade.
• Starting from the middle shade work out (build up) to your lightest light and darkest dark.
• ...and like you said, practice, practice, practice... you'll get there.