How to draw diagrams is largely artistic choice.

The one *mathematically based rule* I can think of is that **pullbacks should always be parallelograms**.

The point is that pullbacks capture substitution, change of base, etc., so that they translate on part of a diagram into another.

The word *translate* there has a deliberately double meaning: the linguistic one and (so long as you use parallelograms) the geometrical one.

On second thoughts, this argument applies to **naturality squares** too.

Other than that, I try always to draw **adjunctions** vertically, so that the left adjoint is on the left and the right on the right.

OK, so maybe there is more than one rule.

Happy commuting!