Don't be the "talker". You know, the dude (it's typically a guy) who is nervous but doesn't want to show it. He just yacks on and on about where he's dived, in what conditions, how deep, what he's seen, etc, etc. And we all know it's bunk especially when he puts his wetsuit on backwards.
If you're nervous, it's OK! If you've not dived in 3 years, it's OK! Don't blow smoke, just be you.
Yup. That was me. I'd like to think I've redeemed myself over the years. I'll have to ask.