When I start a new document, I always begin by adding a few guides:
width/2
width/3
width/3*2
same for height
Some people may even want to add more guides than that.
It would be awesome if there was a way to add halves and thirds, maybe quarters by a simple click, or alternatively, a way to save guide setups (with 'h' and 'w' as variables, since not every document has the same size, of course). Another alternative would be to simply have a few best-practice s