There are two topics it's commonly acknowledged that you steer clear of in polite company: politics and religion. And for good reason; they can incite heated debate, particularly when fuelled with alcohol, and nobody wants that at their birthday drinks. But I believe there's a third subject we should also exclude at social gatherings, and that's what people do for a living. It never delivers a positive result.
It starts off the usual, safe way, "So how do you know Jeremy?" "We've recently moved in next door, you?" "We were at university together." A bit boring, but harmless. But this is where you have to be very careful because quickly it can lead you down the route of, "So, what do you do?" Oh, how I dread that question. Why do people go there? A potentially interesting and fun conversation shot dead right there on the spot. The very best conclusion to such an exchange is that you both come away with a rough understanding of what the other does for 40-odd hours a week to meet the mortgage payments, and have made a new business contact (yippee, fun party, huh?!)
But, much, much worse, at the opposite end of the spectrum you find yourself desperately fishing in your panicked yet oddly bored brain for a fascinating response to, "I'm an IT Project Manager" or "I work in accounts and studying for my CIMA." And you, the usually articulate and witty creature that you are, the absolute best you can come up with is, "Really? That sounds so interesting, tell me about it." And, oh God, so it begins. That poor bastard who was so looking forward to a night off has to explain his job to someone whom he highly suspects doesn't give a shit, while you scan the room for bowls of crisps and make all the essential polite noises, and the pair of you jointly and silently pray for something, anything (a birthday stripper, a ground tremour, an excitable dog) to come along and end the excrutiating pain.
As a sidenote, if you meet an Office Manager at a party and end up making her talk about her job (shame on you), PLEASE don't ask her to explain in detail what her company does; it's like a Saturday night showing of Endurance watching her try to recite the corporate brochure after three strawberry daiquiris. She MANAGES the OFFICE. It's an office; they're all the damn same to an Office Manager. What else could you possibly need to know?
So my advice is ask if they've seen the latest blockbuster movie, ask them what they like to do at weekends, ask them what they've done today or are doing tomorrow, what was the last gig they went to or CD they bought, find out about their hobbies and interests, what sports they play or watch, their favourite restaurant or food... And watch their faces light up, see how animated they become. And this way there'll be much less tension, there's a good chance you'll find it interesting, and you'll learn something about the REAL them, and they about you.