Besides attending live drawing classes I also took up an online program called “Draw a box”. It’s free, with optional donation, and a large reddit community to get feedback from. While I intuitively had a good sense of space and geometry because of my training as an architect. It still was holding me back to draw better from imagination. The lessons are designed to make you think in simpler geometrical forms to assist you in what you want to draw. While contours, gestures and proportions are invaluable foundation skills, learning to think in many shaped boxes helped me to draw better from memory and imagination.