(Read other comments, good advice.) Left, right, straight ahead. Middle crowd, one person at a time. You're only talking to one person of the group at a time. Look left, see that one? Talk to them for that side. Look straight, repeat, right, repeat. Looking left, find them again, talk to the person next to them or just a few away. Straight, repeat, right, repeat. You're speaking because you're knowledgeable on the subject. Expect questions and not only questions, but ones you may not have an immediate answer for. It's up to you if you'll hand out a way to contact them with an answer after the speaking engagement. Recommend a throwaway email for said purposes. Pay zero attention to those who are "not into what your talking about." These people may be there specifically for the person next to them. Not everyone is there to see you. Good luck