Have your introduction ready. This is a pleasant sentence or two; it's not your elevator speech. You are socializing, not job hunting.
Wear your name tag. Place it on your right hand side so that it is in the line of sight of people when you shake hands. You can use the person's name when you introduce yourself and it will help you remember it. Sometimes, a name tag can help with the conversation. Knowing the person's company or location can start a conversation.
Move around the room. You want to meet people. So keeping moving and speak with as many people as you can. Look for people who may be alone. Don't stay with the same people.
Make eye contact. A smile with eye contact will let people know you are open to meeting them.
Pretend you are the host. Introduce yourself to others and introduce people you are speaking with to others.
Reintroduce yourself. If you see someone you've met before, use your name as you greet them. Don't make someone struggle for your name. If you see someone who has helped you, acknowledge them.
Small talk is all you need. Ask people questions or talk about what you have in common – the event, venue, food, sponsor, the activity you are attending.
Just because you have a purpose for attending the activity you are attending, doesn't mean you can't have fun. Enjoy yourself. You can follow up with everyone you met tomorrow. You won't have that opportunity if you don't meet anyone. Working the room is a step in the networking process.