I would agree with some of the points in everyone's posts so far. I believe that God is sovereign but not an interventionist to the smallest minutiae of human affairs. He has made a world that has order, cause and effect. Just as the planets in our solar system revolve around the sun, when we sin the natural outcome is death. Sin is also destructive (that is another one of its effects). You also have to remember that God not only controls things but allows them as well, to admit this is also to admit he is not a stringent interventionist. He does control everything in an ultimate sense, he does not control everything in a dictatorial sense: meaning when I spill a cup of soda I don't think he is the cause of it.
I like to think of God as a computer programmer, though no comparison can be perfect. He sets everything up to have exactly the same results, every single time (order), he only needs to interfere when he wants (lets say to make an update which I would equate to prayer. He can do other things that are to his pleasure as well that have nothing to do with us) or when he feels he needs to (lets say to remove a virus). He is still sovereign over the program because nothing is done without his agreeing to do something, but he is not causing everything (he does not cause viruses, though he could).
God does not author sin, he offers freewill, and he allows things to happen. These three truths alone prove that God allows allot of wiggle room, why else would he tell us to pray? So in that opportunity to pray He is also allowing us to ask for things that He would be pleased in doing so much as it is in accordance with His ultimate will for our lives, he will flesh out the details of our future.
You should also remember that God may put it in our hearts to pray for something, so that when He answers it may result in praise.
2 Corinthians 1:11 You also must help us by prayer, so that many will give thanks on our behalf for the blessing granted us through the prayers of many.
