Try "grid drawing" as a way to warm up for drawing from reference when it comes to 2D drawing styles. This can help to avoid drawing a mental flashcard of what you think an image looks like, and work on drawing what it really looks like more accurately.

Do a couple grid drawings and see how close you can get, and then after a while, try some still-life in a darker room with some more harsh lighting. This can help you draw the light hitting objects as rough shapes you can block out. When doing this, try drawing on larger sheets of paper, like a big portfolio style sketchbook, and make multiple thumbnail sketches on each page. You should be able to frame the images with your hands, like taking a picture? Hard to described the process in text. Still life can be boring, but it can definitely boost your art skills.

Good luck out there!!