I always have a melee weapon in slot 1, even though the only character I ever play is magic. 2 and 3 are always magic weapons, along with 4 once I can vacate a hotbar slot, 4, 5 and 6 are tools- just 5 and 6 once I get a hamaxe, 7 is the Magic Mirror, 8 is Wood or the Rod of Discord when I get it, 9 is torches, and 10 is miscellaneous blocks, or the Flare Gun once I get it, or a mount summoner once I get it.
Said Flare Gun is always in my inventory, even though I have a Wisp and am way past caving at all.
I never use the Builder Potion or building-enhancing accessories, even though I really should.
I always give smaller rooms to the NPCs I don't like.
I have a kill-on-sight rule with the passive creatures.
My chests always have to be placed in a neat rectangle with uniform rows and columns.
I have designated spots in my inventory for collecting gel, fallen stars and mushrooms, even though I just throw out mushrooms once they make a full stack.