I’d like to push designing in black and white first a little further: add the additional challenge of doing so without the use of any borders. If your design feels balanced, proportional and hierarchical in B&W without any borders, you got great design, and the important parts covered.
Another way to harden a design is to keep asking why, regarding every little detail. Like why is there a 17px bottom margin there? If the answer is “it feels right”, it means it is accidental design, not systemic design.