For some problems, worry can be useful. Worry helps me plan ahead. Not only does worry help me create an action plan but also a plan B and plan C, just in case. However, eventually I reach a dead end where the worry ties me in knots without generating any productive results. That's when it is time to trot out the serenity prayer: Grant me the courage to change the things I can, the serenity to accept the things I can't and the wisdom to know the difference. (And yes, this is easier said than done!)
Over the years, I have encountered more and more situations that I don't like but can't change. Eventually, I saw the wisdom in accepting reality. No matter what I want, some things are beyond my control. My only choice is how I respond - worry, anger, or acceptance. The universe continues in its path no matter which one I choose, the only difference is how I feel inside. When I get tired of banging my head against reality, I am ready to accept that some things are beyond my control.
Recently I discovered a third option - to accept that sometimes I just need to worry. Acceptance is a nice concept (and easier on the nerves) but if I'm not there, I'm not there. Worrying about my worry is even less productive than just plain worrying. Instead, I try to relax, accept the worry and realize that this too will pass.
If you want help managing your worry, check out the resource page on Worry and Stress.