In general when we paint we need to go from light to dark. avoid black pigment - try using compliments to shade - let shadows go dark red, purple or blue.
To set up your painting put leaves on newsprint so you can see the shadows against a light color. To make a left painting - use the same skills you did for the apple painting - draw, plan for where the whites will be, start with yellow, then add reds and blues and finally browns. Do details last. There are a lot of videos on YouTube you can watch if you like, but they share the quality of going light to dark, general to specific.