These techniques are good if you need a bit of a kick start to get going.
1. Write for ten minutes about anything. Use an egg timer to time yourself if you like, but you'll probably get more written if you don't - getting going is usually the problem, not keeping going.
2. Give yourself permission to write rubbish. Brilliant writing in your head is worth less than the grottiest bit of writing on the page. Remember, you can always make it better later - that's what editing is for.
3. Don't write chronologically. If you're getting stuck on a particular scene then jump to a scene you do fancy writing. There are no extra points for writing in a particular order, all that matters is the finished product.
4. Close your eyes and visualise the scene. Think of the details - the location, the weather, the people. Then describe the scene, using the 5 senses. Hopefully you'll get started and then keep going. And if you can't keep going, then you've got some useful description that you'll probably be able to use anyway.
5. Team up with a friend and arrange to swap word counts on a daily or weekly basis. Even better, be part of a group where you have to announce your word count. It's amazing how the prospect of confessing to not having written will inspire you.
Most of the time getting over writer's block is a question of overcoming inertia; once you get going you can't stop writing. I'll look at more serious blocks tomorrow.