How large of an audience? The presentation I give to 12 students in one hour will be much different than the one I give to 300 students in one hour.
If I were given the above task--plan a presentation for a large group of students--both current cyclists and not-yet-cyclists--with one hour to speak, it would look something like the below.
minutes 1-10: introduction about my own organization, and the locale where these students are. talk about some bike resources like their on campus stuff, bike paths, emergency numbers, etc.
minutes 10-20: general bike safety, "cyclists fare best when they act and are treated as the driver of a vehicle", hand signals, a BRIEF list of do's and don'ts. perhaps go over some tricky intersections or other problem places in your region (bike path through a pedestrian area on campus, "that one intersection", the place where the bike path comes out of the tunnel and into the road...etc), and.
minutes 20-30: explain the "ABC quick check" (_A_ir in tires? _B_rakes operational? _C_hain in place? quick bounce from about 4-6 inches, make sure nothing's falling off the bike...do this EVERY TIME you ride, until it becomes natural.
minutes 30-45:how to change/fix a flat tire. briefly explain the differences between Presta and Schrader, and that riders should know what they have. use this time to plug your program and any mechanical teaching resources you or another group may offer.
minutes 45-50: how to effectively lock a bike. do's and don'ts, go over several types of locks.
minutes 50-60: questions from the crowd, follow up, list those resources again, plug your own program.
if you can cover all of these topics in an hour, you'll have covered most of the basics, and probably found yourself rushing through most of it.
in short, an hour is not much time to go over "everything", but you can hit some of the main points in a meaningful way.
good luck!