Surround yourself with creative people. Humans are social animals. You'll be inspired when other people are inspired. The creativity will remain high when you work or befriend people who inspire that creativity in you and in your work.
You find it especially helpful if you befriend people who aren't in the same field that you are. These people can give you perspective on your work that you wouldn't get from someone who is saturated in the same ideas that you are.
This is another reason why it's so important to do things outside of your comfort zone. That is where you'll meet people who challenge and inspire creativity in you, people who think differently from you.