Just like the rest of any speech, you need a plan to finish it. Like almost all successful efforts, you need to prepare, practice and believe in your conclusion. There are several elements that should be included in your conclusion.
1. Remind them of your credibility.
2. Remind them of the importance of your topic to them.
3. Go over the main points of the speech.
4. Create some memorable device that will help them retain what you've said.
There are many places on the internet that can aid you in constructing a plan for your conclusion. The link included here is merely one example. The greater the care and preparation the more likely your address will succeed.