I much agree with what the others had said, generally it's easy to start talking to people by striking up conversations about guns, equipment, etc. You shouldn't be standing around on your own for two long, as it's not like paintball where each team has mini-teams of people who came together, and there's no communication between. Airsoft players generally play at a site regularly, whereas players at a paintball site will often only do it on odd occasions (like stag parties), so will have little interest in meeting new people while they're there.
That said I found it a little tricky at first, and not everyone is good at approaching groups of strangers. I found it got easier once I stopped wearing full-face protection, which sounds strange. When I first started I wore a balaclava and SWAT style helmet. Eventually I moved on to just eye-protection and a baseball cap, and I found that more people were approaching me in the safe zone because they recognized me from the field, and it's easy to get involved with what other groups are doing when you're actually in the game.
Not that I'm recommending wearing only eye-protection if you're not comfortable with it, of course, but I felt it was worth a mention.