Great work! And you're right, design "fundamentals" are a lot less tangible. For me, good shape design is at the core of good design- and your list of principles are good guidelines to get there. I had a go at your first set- trying to simply push the shapes and contrast the props amongst each other. It can be as simple as making one taller vs another wider. Tapering up vs tapering down. Making one big and one small. You have good designs in general, which is why I think your question of clarity arises. To make them more clear- think about what your intent is for each prop. Lock onto the qualities of the design that make it more individual and exaggerate them. (You can always tone it down after.) I love the Cerberus idea- stuff like that is clear because it connects the function of "mythological guard dog" to "treasure chest" and it make sense. From there you want to make your shapes reinforce that message/intent. My pass on it was pretty simple but maybe there's an iteration where the top is just three huge dog heads and the legs underneath the chest are paws. (Just brainstorming another way to integrate "Cerberus" into "treasure chest.") This is where design can get really fun when we have interesting purposes to justify and give meaning to interesting shapes. Clarity in design is showing intent! But have fun trying different ways to get the message across!