One thing I learned whilst drawing vehicles of any nature; is to look at each section of a vehicle as an individual piece. For example: the track system on the above Sherman. The front treads by themselves are 4 separate layers. Each are focused individually and placed together to make a whole. The bogey system is also 4 pieces. The main unit that holds the wheels, the wheels them selves, the arms and the spring. All that adds up to what you see before you.
So when a making a piece focus on one section at a time, then in that section divide it up into layers that you can work on.
I hope my explanation is helpful @Coco . If you would like a different analogy I would be happy to give another
