An instructor I have a lot of respect for once told me "the only two places where people seem happy to get less than what they pay for are the dentist's chair and the classroom". I've seen some phenomenal lecturers who have spent 30-40 hours putting together a 3-hour lecture and students will still be on facebook/twitter/reddit/snapchat/whatever in class. In my tutorials I have the ability to control cell phone use, but I'm not about to ban laptops. At the end of the day, I've found it easier to make peace with the fact that, no matter how good your presentation is, it's impossible to get everyone to pay attention all of the time. If someone wants to look at their phone rather than listen to me, I'm pretty much okay with that, so long as they aren't distracting others.

I've found openings to be really key to getting people to pay attention. In the first ~10-25% of the presentation, I try pretty hard to get the maximum number of people on board. Some will stop focusing at some point along the way, and there will be some people who will never start paying attention, regardless of what I do, but I like to spend the first little while trying to engage the audience as much as possible. Humour is super effective in short bursts, but difficult to sustain. Setting the stakes is always key. Narrative can really keep things moving and keep people engaged in the longer term.

Public speaking is definitely a tough skill, and not one that's easy to develop without putting yourself out there and failing spectacularly at least a few times. Lots of people suffer from pretty intense anxiety about it, and different people deal with it differently, but "nerves" can be paralyzing for some, particularly if they're coming from environments where being outspoken is shunned in some way.