Sometimes the most difficult thing to do is free your mind and start writing down ideas. A really simple fix to generate movement and help your thoughts flow more freely is to just start writing.
Think of the first thing that comes into your head or take inspiration from what you see around you. Then use associations to write more and more until you have filled a whole page with your ramblings. It can be relevant or complete nonsense. The most important thing is that you are loosening your thought patterns ready to start creating.