It's tough. There's no quick fix. But part of it is to change your behavior.
1. Think of the things that make you happy. If they're thoughts and feelings (like holding your child in your arms) keep those thoughts fresh in your mind. Make them into a "happy place" you can peek into now and then. Eventually, these thoughts will become like a mantra and help you relax and smile.
If it's things you do, find time to do them. If you don't have time, make time. Life is too short to sacrifice the things that make you happy. The things that get in the way are always in the way because they are always there. Which means they can wait for you to get in a short drive, or an hour or two with your favorite hobby.
2. Now that you have your refuge set up, it's time to address your stress.
What's upsetting you? Make a list if you like.
Now, what can you REALLY effect? War in the middle east? I don't think so. Separate your list into things you can effect, and things that you can't.
What's on your 'I can do something about this' list? Take each problem and break it down until you can come up with a plan to fix it. You don't have to fix it immediately. Just get a plan. Even if it's something like "Get a promotion into <this position> at work." Having a plan, whether immediately realistic or not, will make the problem seem less like a mountain and more surmountable.
3. Now for that other list.. The 'I can't do shit about this' list.
This is the tough one. Here's where you have to learn to change your behavior. You need to tell yourself that you can't fix it, so you can't worry about it. It'll be tough at first. We are genetically and chemically predisposed to follow old thought/feeling patterns and stay there. We are essentially *ADDICTED* to the ruts we're in. So it take effort to climb out of them.
So you have to watch yourself. Whenever you find yourself getting worried about something your can't effect; *stop yourself*, then remind yourself that you can't do anything about it and to let it go. The more you do this, the easier it will get, until you've changed your behavior.
4. But what about the future? The future is coming whether we want it to or not. Remember 2 and 3. The things we can effect we can deal with. The other shit doesn't matter. Worrying about hitting a tree won't make the tree go away. But focusing on the car and what you can do with it might get you past the tree.
So to simplify: "Don't worry, be happy!" It's a stupid line from a stupid song. But in essence, it's a little bit of truth.
Oh, and I almost forgot: STOP WATCHING THE FUCKING NEWS! Might as well declare the world doomed and suck on a tailpipe if you pay attention to the news companies.