Personally, I come up with ideas the moment I wake up. I recently started writing ideas down for future reference, though I'm not sure if I'm ever going to use them. I often don't finish art at all, because while painting I will get bored with it and start something else. I actually wish that I could have artist block for a day, I imagine it is such peaceful bliss.
I hope this doesn't sound like I'm boasting...
BTW, I'm going to start uploading my real art soon.