1) Don't fight it, switch off and relax your brain for a while, even just watching some easy viewing tele or socializing.
2) Use Twitter. Follow industry related people / magazines / organisations / fellow writers and bloggers. I guarantee that something someone writes in your timeline will spark an idea.
3) Watch / do / read / listen to something that inspires you. It puts you in a better place to think about the things you enjoy. Music lyrics help me a lot.
4) Make lists - five things to do when... / three tips to help with...
5) Write a word on a piece of paper. Imagine a situation around that word.
and a cheeky 6) Go to your nearest coffee bar, hide behind a paper or magazine and listen and observe the going ons around you...
Notice I didn't mention exercise. This is a great way to energise not just your physical being, but your mental state too... However, who exercises when they're depressed, fed up and tired because the words aren't flowing? Certainly not me!