One of the things that always deterred me was having the supplies (but put away, neatly, in a cabinet). Art is messy and I am more inclined to do it when I leave stuff out and it is handy—if I have to go track everything down, it isn’t going to happen.
I also like doing art (read making the mess) in the rooms where other people gather. I don’t want to be off alone in a different room to do art (I do when I write, however). So, it takes household members who are willing to tolerate the mess and the moodiness than can accompany artistic birthing. Sometimes I pace, with a paint brush hanging out of my mouth until the idea is better formed in my mind.
The best thing to motivate me is an image that is incredibly significant to me—maybe the way the light hits or the colors in a photo or some other feature. A friend of mine gave me a book entitled “A Sketch a Day” and it is like a diary that allows me to keep track of ideas as they pop up. There is a great website (although a bit slow to load) called Wet Canvas. They have events called WDE (weekend drawing events) wherein a regular posts 16 or so photographs for inspiration and you have a limited time to interpret one of the photos and post your work in progress and at the end.
Wet Canvas also has places to post work to get critiques—I have gotten a lot of helpful feedback from VERY experienced artists with tips and pointers. I have found the critique on point and polite.