Here's how I set up canti-brake pads. Cut a business card in half long ways and then bend what's left in half. Form that into a "u" and place it around the rim and up between the rim's sidewall and the back end of the two brake pads. Squeeze the brake handle slightly and while holding pressure, loosen the fixing nuts on the pads, position the pads, pull the brake handle in to toe-in the pads, and tighten the fixing nuts. Both pads will be properly positioned and toed-in. It takes a bit of a deft hand and patience but this approach works well.

And yes, in my experience and has been mentioned, more toe-in than less is better.