When creating each mechanic, and level to display them in, I went through a number of steps. First I decided what mechanic I should create. Second, I broke down what systems were needed for that mechanic. Third, I checked if there was any other sub-mechanic or another mechanic that could use this system to demonstrate what it can do.
For example in the screenshot on the left, you can see the "Puzzle Mechanics" level. In this level, the first thing I made was a simple push a box into a ditch to cross it mechanic. But then I realised I could also use a smaller version of the box as a key for a door so I then created a button mechanic that was pressed when a box was pushed into it and then a door that would check its selected button and when it was activated the door would open.