Speak only to individuals. A group is composed of individuals. When you speak to individuals, the others in the group feel you are also speaking to them; when you speak to a "group" no one feels you are speaking to any one person.
Know your subject inside and out, because this builds confidence. Audiences like a confident speaker - after all, they have "elected" you to speak while they listen. Audiences like certainty; someone who is confident instills confidence in others.
Never worry about what you forget. The audience does not know you forgot, but they do know what you did say.