When I presented to a conference and was waiting for everyone to shut up, I said "if you don't sit down now I'll have to tell my duck joke". Of course some one said "go on then" and I had to tell it. They laughed, I got their attention.
Also mention coffee, you don't have to serve it, but if you see them flagging, just mention coffee and watch their reaction.
Smile, don't say "I'm nervous/ doesn't technology suck", look them in the eye, move around if you can, use a cartoon or striking image in the first slide.
Good luck!