Experiment with values
If you’re struggling with your lighting, most likely it’s a value problem (lights and darks). Try turning your image to greyscale, and look for clear silhouetting of shapes and clear, consistent light sources. When it’s time to move back into colour, try to keep things simple by only considering the temperature of the colour. If you do nothing other than get warm, cool and neutral colours to feel right relative to each other, you’ll be surprised at how accurate your colour becomes!