Toe in is set so the leading edge of the brake pad hits the rim first.
I use a thin piece of card from a cereal packet folded in half. Loosen the retaining nut for the brake pad and then trap the card between the wheel rim and the rear end of the brake pad. Adjust the position of the pad so it meets the rim correctly, then squeeze the brake lever tightly so it compresses the card against the rim while you tighten the retaining nut again. This will give you appx 2mm toe in and can help prevent squealing and shuddering. Repeat on the other 3 brake blocks.