It's important, I feel, to plan for the long term. How things are done in the earliest stages of a project can have a great impact on the later stages, for better or for worse.
With this in mind, I'm trying to make sure that all our work in pre-production is done in ways that will make our lives easier later, even if it costs a bit of time now. For example, the first image, a reference ensuring level construction in Unity is standardised. Placing 1,1,1 as the rear-wall corner point means that each wall occupies the 0-coordinate on each axis, and gives us the flexibility to use levels of varying size without making the coding any more difficult than it needs to be. To work with this, terrain blocks, hazards and so on will also occupy standard cubic volumes and have their pivots placed in the rear corner – that way, setting an object's position to 4,1,2 will place it in the 4th column, 2nd row, at a height of 1 (on top of the ground). Easy to predict, easy to understand, easy to work with.
On the right is a sketch I made for the GDD, ensuring the operation of the fall-height mechanic is as clear as possible. Miscommunication causes problems, so good documentation and standardisation is essential in making sure everything runs smoothly!