1. The George Costanza Method
Named for the life choice that George Costanza made in Season Five of Seinfeld. His life wasn't what he wanted it to be and no matter how hard he tried doing the "right" things to get it to where he wanted, he got nowhere. So, he decided to start doing the opposite of what he instinctively felt would lead to the results he wanted. If doing what you think should work isn't working, do the opposite. Spend some time doing the exact opposite of what you usually do. Obviously, this won't work in every situation, but in the context of creativity the stakes are low. If you're designing a cover for a heavy metal band, try making it look like a hallmark card. The best part, if doing the opposite doesn't work, you can always stop doing it.
2. Change Your Commute
Most of what you do in a day is so ingrained in you that you don't actually think about it. For a lot of people the best example of this is their commute. They go into a trance-like state as soon as they get on the road and when they get work, they couldn't answer a single question about the trip. In fact, I know a lot of people who have left the house on a Saturday morning with the driving somewhere fun and then ended up at their work feeling slightly embarrassed. (I'll admit it, I've done this myself.) This one is easy. Even if it takes a little longer or is more inconvenient, change your path to work for a few days. Drive down fresh streets, stop at different stop lights. You'll be amazed at all you notice and you might just discover a faster route.
3. Calling Things By The Wrong Name
This is an improvisation warmup invented, as far as I know, by Keith Johnstone. This exercise is loud and funny looking, so you'll want some privacy. The best place to do this is in a room you're familiar with, maybe an office or living room. Take a few minutes to just point at objects in the room and say the wrong name for them. If you point at a lamp, call it a giraffe. If you point at a book, call it a salad. If you start to get uncomfortable just keep going. Some people report that this actually makes them lightheaded. A usual side-effect is that everything seems brighter and your awareness of your surroundings is increased.
4. Write WIth the Wrong Hand
This is another method that seems stupid and simple, but can yield amazing results. If you are right-handed, write about your problem or area of exploration with your left hand. If you are left-handed, do it with your right. This makes your conscious mind have to think about the process of writing applies the opposite side of your brain to the problem. This one is especially good if you buy into the whole right-brain/left-brain dichotomy.
5. Listen to a Radio Talk Show That Pisses You Off
Sometimes you just need to light the fire of passion underneath yourself. That can be hard when you aren't passionate about what you're working on. So, whether it's Rush Limbaugh, Al Franken or the guys on Car Talk, find something that really makes you angry to listen to while you're working . Cursing at the radio helps to physicalize the passion.