You will have to reverse your usual thinking in terms of shading and do everything opposite.
Place an object in front of you. This is an “observation drawing” exercise as well. No photographs or pictures!
Erasing white pencil is not as easy as erasing your regular pencil. So, if you don’t feel confident enough to start with a white pencil right away – you can use your regular drawing pencil to sketch the object. Include all the details!
In your regular drawing you would start shading with the darkest areas. In this drawing you start with the lightest areas.
In regular drawing you shade the areas that are darker. In this drawing you shade the areas that are lighter.
Work with small strokes. Don’t press hard on the pencil – you can always go back and make things lighter, but you’ll have harder time to make them darker again.
Keep your pencil sharp.