Create for yourself. Write the song you want to hear, or the book you want to read.
Strive toward excellence, but don't become obsessed with perfection. Perfection is not only impossible, but boring as well. Some of the best records or books have obvious mistakes or flaws that make them all the more endearing.
If you're stuck, try changing your surroundings.
Always be on the lookout for new sources of inspiration.
Playing with your band or working on your novel should be fun. It won't always be, but the more that it can be, the better.
Patience and persistence. Patience and persistence. Patience and persistence.
Do something - anything - every day, even if it's just playing random licks on your guitar for five minutes or writing a single paragraph.
Remember: happiness is a state of mind, worrying is a waste of time, and sometimes, you just gotta say, what the heck. And go with it.