The first model I did - acetate & wood - was based upon a sketch. One way I like sketching is to just through shapes together onto a pile, “read” the pile, and then sketch forms which appear. Not quite as random or procrastination bound as you may think.
I also had some sticks, and some modelling clay which I had yet to use (bought it during the Carousel, that seems so long ago now). Used some of the clay a as a base to stick the sticks into, and went to work playing with shapes. Not entirely displeased with the outcomes.
Lastly, we had a modelling workshop with Sim (sculpture & welding tutor), who showed us how to do a basic plaster relief. Clay has admittedly never been my strongest suit, but I thought this came out rather well.