My administrative assistant sometimes says, "That sounded better in my head." It makes me laugh, but it also states clearly the basic problem of communication: How do you make sure what's in your head ends up in theirs?
All you have to work with is words, so here are a couple of suggestions:
1) Make sure your words do their job: communicate the right meaning. My Tac Officer said, "Use precise terms precisely." For me, "Start at ten" means in your seat and ready by then; to our Sales Manager it means start getting ready to attend the meeting at ten - "In your seats at ten" works better for him. "Fix" means repair to a maintenance man but to an infantryman, it means to hold in place. To a paint-maker, it's a noun that means the stuff you need to correct a batch.
2) State your point in a single short, declarative sentence. "I want you to be on time" works a lot better than "You know, when the team has to start short-handed, there are a lot of outcomes that affect a lot of people." Say it the way you want them to get it.
That's it: Just use the right words, and then don't use more of them than you have to. Oh, and then ask enough questions to make sure they understand. The burden is on you to communicate, not on them.
There's a great conversation on the value of speaking skills over at Leadership Freak. If you've never been there, just Google it. You won't be disappointed.