A great exercise that I mentioned in my article on finding and maintaining creativity was writing music every day. What does this entail? Does this mean you should start and finish a new song every day? Work on just one song over a long period of time?
The mindset you should have is that you will sit down in front of your keyboard, sheet music, studio, guitar, jug or whatever you have to make music every day regardless of what ideas you have. It is important to remember that what you actually make is irrelevant. You could be working on one polished song, making a different little sketch each day, or just recording weird stuff that comes to your mind. Just as long as you sit down and do something every day.
As soon as you stop thinking about results, you can start thinking about making something. Think of it like daily exercise. When you go for a jog, you don't really care about the destination, you are simply doing it to condition your muscles and heart. You do daily creative exercise to condition your creative abilities and your neural pathways. You should not be worried about the result of your efforts. No one is embarrassed about running in a loop every day and getting nowhere. So too, you shouldn't be embarrassed about the random crap you make every day. No one has to hear it but you.
I have often paralyzed my music output because I would worry too much about making something professional and polished. I felt that anything I started wasn't good enough, and soon I would just get in a rut, making pretty much nothing. Finally I decided that this was lame and making somewhat unpolished music is better than making no music at all.
It is particularly fun to simply try to make something new every day. Sure, a lot of it will be crap, but it will keep forcing you to come up with new stuff, which means new neural pathways for you and more creative energy. Plus, you'll quite often stumble on something awesome and you'll want to expand it into something more complete.
So here's my challenge for you: sit down with your music making equipment for at least an hour every day and make sure you have at least something by the end of your session. I don't care what it is, and neither should you. You will discover all sorts of new stuff this way. In fact, go do it right now.