For concerts what I do is this:
Get as close as you can, obviously, I feel that the closer you are the less light falloff will occur before it reaches your lens, maybe I'm wrong and that's not scientific I just feel that way.
Always shoot in Manual, AV mode will not account for the situation and will often try and over expose the shot. Start with 2.8 and a shutter speed of around 1/200th depending on the light, then gradually work it up or down. Remember you can always half correct underexposed shots, but if you blow out the image with too much brightness you can't correct that.
Zoom in on the shot to check focus, when focus starts to go you've gotten the shutter speed usually too slow (around 1/60th). Shoot in RAW, you can always work better afterwards with that. I don't know what your ISO capabilities are, but depending I would say keep your ISO at 800 or above, if it starts to look ridiculously grainy, lower the ISO. The Truckers have an open photo policy, so take your time, you have all show. I use autofocus, but then again my lenses focus more or less correctly. Try setting a static focus point and using that instead of letting it autoselect for you. IF that doesn't work read in your manual on how to calibrate a lens for a camera.
Now following those guidelines depending on the lighting you are going to get different results. These were shot at two different shows, each at 1/200th of a second, same ISO, the worse one was at 1.8 and more wide open than the better one. Point being, sometimes it's a crapshoot and don't be disappointed if your results aren't that good. Some clubs like the 9:30 club I can't get a good shot if my life depends on it (but this weekend I will)
good lighting: f2.8 1/200th of a second
bad bad lighting f1.8 1/200th of a second
For your wife's graduation it will be very much the same method as a concert, except you might be able to go to f3.5 and keep the shutter speed around 1/400th or higher. Test it out on people who aren't important.