A second-hand summary of parts of Rick Rubin in The Creative Act:

When you don't have the muse don't worry about it or try to get it to show up.

When it strikes, push it as hard as you can and be thankful for it.

Don't stress when it's gone, it will come back, and you can't force it to come back.

All you can do is make the most of it when it does hit.^{[alh][ali][alj]}