At first glance this watercolor by Lars Lerin looks like it was painted with great attention to detail, but a closer look reveals that the artist used an economy of means to make the goblet so real.
It's not so much that he was careful and thorough, as that he knew what mattered.
Taking care to put the darkest darks and the lightest lights where they work makes it unnecessary to get all the middle value shapes exactly right. Lerin has an eye for the essential, which allows him to be carefree with the optional.
To see so clearly the few parts of a subject that have to be correct is a tremendous help in translating it into washes and strokes. For us mortals, it takes more than one attempt to sort out what matters most. For homework, find a simple object, like an onion, or a teapot. Use an actual object rather than a photo. Set it in a spot where it is lit by a single light source, so the shadows are not too complicated.
First try painting it in monochrome, using a single color straight from the tube rather than a mixed color. Make sure your choice is inherently dark enough to represent the darkest parts of your subject, like carbazole violet or pthalo green.
After you've gotten to know what comprises a good representation of your apple/beachball, put the subject back where you found it and paint a version from memory.
Bring in all your studies.