1. Go for a walk. Many people find that when they are trying to think walking helps. Walking brings more oxygen to your brain and speeds up the body's functions. It will relax you and help you think clearer and easier. Besides. Even if you still arent inspired, you will get some exercise out of it.
2. Chew some minty gum. If walking doesnt work, then chew some minty gum. The chewing has some of the same benefits as walking, but the big reason is the mint. The fragrance and taste of the mint will stimulate your brain to help you focus and think.
3. Observe. Look at some examples of other people's work. If you are trying to compose a song, then listen to your favorite artist. If you are writing a book, then take a reading break. Observing other people's works will help influence and improve your own style and will boost the inspiration process by giving you some ideas.
4. Get re-inspired. Go back to what inspired you in the first place. It will remind you of why you are doing this and freshen your mind. If you are doing this for your job, then look back at what inspired you to take the job in the first place.
5. Stop. If none of this is working, just come back to it later. There is no use in trying to do it now, especially if you are frustated. Come back to it later when your mind is fresh.
6. Get out. Go out and see the people. Experience life. After all, that is where all ideas are traced back to. Who knows. Maybe the people on the subway will inspire you to make a painting.