I've read, and heard, many times that the gist of a talk's structure is:

• tell 'em what you're going to tell 'em
• [stuff you came to tell 'em]
• tell 'em what you told 'em
• thank 'em and say goodbye

I've experimented with this and have found it's definitely a good go-to formula, especially if you're just starting out.
I do think there's a little more to those last two bullet points, though. Summarize a talk by recapping, yes. Good stuff. Gratitude - a MUST. I believe there's also got to be something between those last two bullets in a speaker's tone or message that sends the audience off with a really great feeling. If I've taught them something, I try to remind them why what I've shared is useful, or how it can improve their life. If I've shared a personal story, I aim to share the positive outcome not only through your message but also through your voice and energy.  

" I've learned that people will forget what you said, people will forget what you did, but people will never forget how you made them feel." -Maya Angelou

Think about how you want your audience to feel.

Seal the deal on why your talk was worth their time. Then thank them and say goodbye.