How do you make sure your audience never loses focus on what you're presenting?

I'm pretty good at reading body language. It has helped me very much.

How do you block out distractions when you are trying to multitask different people and activities at the same time?

How do you approach a situation when there are more than one person you are talking with but only one person is trying to focus while the other is trying to make the other not pay attention?

How can you grab one's attention while trying to draw them into what yoiu're sayng if they were never interested from the get go?