When drawing and painting, you can really make an image “pop” by paying attention to the overall lights and darks of the piece. If you can look at your picture and see that it’s roughly the same value, you should consider darkening the shadows and brightening the highlights. Doing this will add contrast and prevent the work from looking like an undifferentiated mass.
This is particularly apparent when using pencils. It’s worthwhile to invest in a really soft, dark pencil (like a 6b or even a 9b) to make the darks really, really dark. A touch of chalk pencil can touch up the highlights for some extra impact.