Let him know I'm interested?

I met this guy (a friend of a friend) last week, and we flirted a little that day. I'm seeing him again this week at a bonfire (there will be a lot of other people there)-what should I say to convey that I'm interested in him? I don't know a lot about him but I really liked him, and he flirted back so I think he might too. I'm just not sure-what should I say? Also what should I wear? lol