>>5794569Try to find an online model of a ribcage; draw it from different angle, simplified.
If you can, try to find a high quality plate of a ribcage, e.g. from a medical book. Print it, and spend 4/5h copying it with great precision.
Find a few pictures of people's torso; trace the bones, trace the muscles.
If you already know all those thing, then just spend more time practicing. It's a marathon, not a sprint. Get a shower & a good night of sleep instead of burning that frustration away.