You can create cross contours on objects and then draw them, that will help you visualize contours when there are none. For starters get a simple object like a ping pong ball or an egg and draw a line over it that goes all around from top to bottom, then draw it in all sorts of angles. Then you can do the same with fruit, draw many longitudinal lines connecting the top, to bottom of an apple, or draw many latitudinal lines over a banana and then draw them paying special attention to how the contour describes form.

Here are some old drawings I did for the Art & Science of Drawing Course: https://imgur.com/a/VrjZ1Fc