1. Find a challenge group - many social networks like Gather have them and write to the prompt. It works!
2. Find a writing group in your home town and join it. Preferably the one you choose will share their writing every week so you will be motivated to have something to share yourself.
3. Think of a word or phrase, anything, and challenge yourself. Write a story or a poem or even an article around that word or phrase. Don't think about what you will write when choosing the word - just look around you and pick.
4. Read the headlines and/or the current news. Write about something that raises your blood pressure. It can be a blog, an article or even a fiction story.
5. Enter a contest. This one will really get you going if you're up for it, especially a contest such as the National Novel Writing Month (NaNoWriMo) or Script Frenzy where you have a fixed length of time to complete your work.
6. Look at a piece of art or a painting and imagine the story being told by it. You could write a story, a poem or even a whole manuscript!
7. Go through your old work and write a sequel, even if that work is a poem you can follow up on the story it was telling or the emotions it was describing.
8. Take a walk, not only will it help clear your head, but you can work through scenes as you walk, talk out the problems in your piece.
9. Talk about it. If you're stuck on a particular scene or you can't find an ending to your book or story, talk about it. Even if you only have yourself to talk to. Speak out loud so you can hear the scenes, hear the dialogue that is the problem. You are much more likely to be able to work your "kinks" out this way.
10. Find a writing buddy. If you just can't seem to put pen to paper at all, find someone to write with. You can motivate each other in many ways.
Now Go Write!