There's a temptation when you go to a networking meeting to stick with people you know rather than talk to complete strangers. You feel more comfortable, it's not as intimidating, you can catch up.
Aim to talk to 5-6 new people you don't already know. This isn't too difficult, as most meetings are a couple of hours long. Yes, it's great to catch-up and reconnect with people you know but balance this with meeting new people.
If you go with a colleague - split up. You know what each other do - divide your time and speak to different people, you'll cover more ground than going around in pairs.
Talk to the new people who are possibly standing on their own looking a little lost. Introduce them to people you know after you've had an initial chat with them.
Be bold. Go up and introduce yourself to someone you don't know.
If there's a sit down meal involved or a presentation, sit next to someone you don't know. You can swap notes with your colleagues later.
Go to a meeting you wouldn't normally go to. While I like to balance this with not attending every meeting going. Sometimes a fresh environment can bring surprising and rewarding results.