Couple of things, the 10 is the quickest bus to take to from campus to downtown, but it stops at Main and John not Main and MacNab. Main and John is best spot to get off though, so don't worry about this.
If you're on the 10, the stop before John (the one you want) is Queen, which is just at the top a little hill and basically where Hess Village is. You can pull the cord for the next stop right after Queen and get up off your seat right if you're really worried about missing the stop (it will be another 3-4 minutes drive). You can also just tell the bus driver you want off at John and they'll generally be sure to yell to remind you.
When you get off the 10 at John, you'll be on the South side of the street, you'll need to cross main street to the north side and then cross to the East side of John street. You'll then be right in front of the London Tap House (a popular bar!).
Now that you're on the correct corner, walk 1.5 blocks north on John street cross by Gore Park (a tiny strip of trees) then cross King St E and continue another 10-20 metres. You should then see the Yellow / Blue HSR stop sign in that area, that's where the #2 will stop (Stop #1239). If you get to the Greek Palace eatery, you've gone too far. When you're at the #2 stop be sure to make yourself seen. The drivers aren't supposed to stop unless someone is right near the curb at the stop. A quick wave and smile also helps
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Here's a link to the google maps version of the route:
http://www.google.ca/maps?f=d&source...,0.005429&z=18