I'm pretty rubbish socially. At one event, I was getting on okay, established person's name, who they worked for, their role. And then I said, "So is it your first job?" Meaning had she worked in other sectors, rather than was it literally her first job. She was a manager in her late 30s, and clearly unimpressed. I don't know why I didn't phrase it better. (Well, I do - nerves mangled my brain.)
If you're hosting it, then you need to have some idea of what you do (no joke - there's a lot of stuff our company does where I only have the vaguest idea), and be able to summarise that (doing a couple of careers fairs really helped me there - I can witter on quite successfully now.) Know who are the people that you can introduce them to - "Oh, you're interested in private networks? You must talk to John over there! Security services? Let me introduce you to Dave!" This way you can make it someone else's problem by being helpful.
Also, if you have some idea of who's expected and what their companies do, that will help make you look like less of a spare part, and you might be able to ask about things you want to know about the company.
I would say as a woman, avoid ending up as a waitress - but offering to get someone another drink or using a platter of canapes as a prop and to give you some purpose can be an escape plan in desperation. Depends a bit on the catering facilities. At the last event I was at, I had noticed there were little menus on the tables, describing the canapes, so when people were asking, "What is that meant to be?" I was able to explain, "that one's tuna, that's chicken, and that's blue cheese," and that helped break the ice a couple of times.