First, honor your hosts. It's nice, and it displays thoughtfulness. Second, tell the audience what you are about to tell them. This removes humans’ natural anxiety for the unknown. Once you've given your talk, tell the audience what you just told them "in conclusion" so they know it's over and thank them for their time and attention—that's their cue to clap. This sounds simple but lots of people don't do it resulting in many a nervous audience thinking the speaker is arrogant.