How can I get the courage to smile at him?

While I agree with The-Nash's idea of trying to read his body language, I don't know that its really some sort of 'textbook' maneuver. Do you feel awkward when you make eye contact with people you pass in the halls and/or often avoid eye contact with strangers when walking down the street (in some cases its better to avoid eye contact but this isn't one of them)

If you're not comfortable with doing so get yourself used to walking around with your eyes at head level, a lot of people shy away from eye to eye contact because it has an awkward feeling of a sort of intimacy attached to it, so its obviously going to be harder to do it with someone you're interested in.

Things like this are habitual, and unfortunately the only way to change them is stepping outside your comfort zone until you're no longer uncomfortable.

In short, the best way to do it, is to just go ahead and do it. I know it sounds easier than it is, but that's all there is to it.

Go about your day like your in a pretty good mood and have like an - almost smile - on your face, and when you catch his eye, bend it into an easy curious smile, an easy smirk on one side and blink at him twice, like your batting your eye lashes, but easy and graceful - the whole way. Control his smile with the way you smile. Good Luck! If he follows through with mimicking the smile, go talk to him, say "Hey, I'm ___."