Well, I am not religious about my composition nor my improvisations. I do those when I feel like it, so I might say that I only do them when I feel inspired. It is a goal for me, however, to make a point of doing both everyday, for a certain amount of time. I have found that when I sit down to compose, I enjoy using form models and may treat it as an exercise to try my hand at a certain form.
What has happened a few times along the way, I will become completely overtaken by my involvement with it to the point where I cannot sleep until it is done. So, many times, if I will actually finish something it happens within 24 hrs of its "beginning". When I get like this, beyond the inspiration to sit and compose in the first place, I feel almost as though I am simply channelling something through me. Everything is just flowing through me and it is almost unstoppable. I would also call this inspiration, perhaps, for lack of a better word.
I have noticed, however, that this very thing happens with other forms of expression for me as well; poetry, drawing, beading, writing, etc.. I am sometimes inclined to think it is good to wait for that wind which picks up my motivation toward activity, but I am realizing it may be preferable to form habits. I am quite addicted to inspiration, however, and would not wish for a mundane attitude to destroy those possible moments of channelled delights. Perhaps my overall understanding is in dire need of maturation.
m1469