The thing that causes most freeze ups in any sport, is lack of information.
If you don't know what's going on around you, you have no hope at knowing all your possible options when you have the ball, and selecting the best one.
Do this, go on youtube and watch a compilation of a player like Xavi or Zidane, as suggested, and instead of watching the ball, watch them all the time, off and on the ball.
These two links might be useful to many, they definitely were for me.
http://leftfootreflections.blogspot.com ... youth.html
http://leftfootreflections.blogspot.com ... nical.html
The second one is about body shapes, and how it can affect your ability to receive the ball and make decisions, which is also a major cause for mistakes being made or you "freezing up."
When you are watching a player, like Xavi particularly, notice how he always is facing towards the ball when possible, and then he side steps and shuffles to move around, instead of turning and running into space, this is important, because if you turn away from the ball and run into space, for the split second you haven't being looking at what is going on in front of you, which can affect your decision making massively.
Also notice how, while he is shuffling around into space, every couple of seconds he looks around, almost compulsively, this is really important as well, because if you are reading what is happening around you, and you see everything happening around you, and your body shape is best suited to receive the ball, then you will feel like you have acres of space and time, and you will start making decisions without even thinking about it; as Rome said.