Naming ranges is the one on this list that pays off for other people rather than for you, which is why it gets skipped.
A formula full of cell references is unreadable to a colleague and unreadable to you next quarter. The same formula with names is a sentence. It costs about ten seconds per name.
Second thing that pairs with it: put the assumptions in one clearly marked block at the top of the sheet, all named, and never hardcode a number inside a formula. Every spreadsheet argument I have had traced back to a number buried in a formula that nobody knew was there.