Finding a subject
During my spare time, I find subjects by either sketching my surroundings, or finding something interesting through different feeds and media. This is usually at morning with a bite to eat including a disproportionate amount of caffeine, or at night before bedtime with tea and cookies (just kidding, tea and body parts actually.) Looking through tutorials or how to's of other artists is also a fun source for deciding what to draw, or simply to become inspired to draw. For myself, I usually first look to build out from the inventory of sketches that I make and keep handy. Quick sketches are an easy way for me to note rough or vague ideas that I can return to later and possibly build or elaborate.
If the sketch will just remain a sketch, I do less blocking, and more hatching, line weight variation or shading. Composition also matters to me a bit less when I'm in sketch mode. Some sessions I never get past sketch mode I'm just adding sketches to a stack to finally delete or build out later.
Working Up, Rough Layout
Taking my quick sketches, I begin blocking out solid shapes or masses on various sketches until I make one that I like. This may be from a fresh sketch that I make on the spot, or going through my inventory of sketches as I mentioned above.
When I block out shapes on a sketch, I try to think in terms of silhouettes and / or shadows. I keep going until I find something pleasing. I adjust the sketch placement on my canvas as needed by scaling and cropping, and continue with blocking, examining the composition.
I sometimes also use the harmony project, and Alchemy as shortcuts to jumping over the sketch phase. I can't say enough about these two tools. They are great for exploration of the early states that images exist in, and they do it well. I would say it's like being able to work at an embryonic state of an image for a long time without fear of building it up too much and loosing the exploratory mode. Once you're familiar with these tools, one can explore sketching, mass, and composition or all of them at the same time.
With only 2 hours in a day for making art I work quickly, so my images are generally shallow with little if any mental depth or narrative. While the subject may be simple, my recent tendencies have been to entice the viewer to be a bit more engaged with my images. I try allowing viewers some room to create their own mental spaces and lines within my drawings.
A bit more on how I work on my roughs when I go into painting mode. Some different ways I go about finishing art created on my Nexus 7 tablet.