How to keep yourself motivated while drawing
"How do you keep yourself motivated while drawing?"
For each artist the answer to this question will be a combination of different things, depending on what the artist wants to achieve.
Drawing is a physical, as well as mental, activity. And like any physical activity, you'll reach a point where there is a build-up that presents a barrier through which you must push yourself if you're to reach your goal. The goal has to justify the momentary pain you have to overcome. It's also necessary to rout out the things that can demotivate you: boredom and frustration are two of the biggest.
When I decide to create a finished drawing, the subject has to hold my interest and contain some type of challenge I must meet in order to consider the drawing successful. Setting yourself up with a challenge can keep boredom at bay, but it invites frustration as you come face-to-face with your current limitations. Frustration can only be overcome with perseverance and practice.
Sometimes I will draw as a warm-up to another work in a different medium - watercolor or acrylic - and my motivation there will be to discover what exactly it is about the subject that inspires me and how best to compose and render it in the final medium.
I have a tendency to use my body wisdom rather than my intellect when approaching a work of art - other artists will have a clear concept in mind, but I tend to follow my senses - so I cannot always articulate why I want to draw a thing. I like it to be a mystery to uncover in the drawing process. The unfolding mystery keeps me motivated.
The biggest roadblock for me and many others is when I get to a point where I'm dissatisfied with the drawing. Anya Deason describes in her answer to this question how she will convert her analog drawing to digital and finish it off there. Another way of dealing with the "roadblock" is to relinquish the "precious" outlook - that you have put so much time into something that you simply must keep going to preserve what you've done. With drawing, you can either wear out the surface with too much erasure or you can overload the paper with too much graphite. You reach a point of no return. It is essential to get over this quickly and start again on a fresh piece of paper.
Sometimes I don't really have a clear idea of what and why I am doing and just get caught up in the impulse to draw. If this happens to you, it's worthwhile to get a large pad of inexpensive bond paper and work out a composition before committing to an expensive piece of drawing paper. A pristine, beautiful piece of paper can be rather intimidating. I also still use a "view finder" to help me with composing a picture from life drawing. Here's a good web page for making a view finder: Drawing Tutorials. I just use an old 35mm slide that doesn't have any film in it. (I imagine these aren't so easy to find these days, but back in the dark ages, we used to have to submit 35mm slides of our works to juries.)
Another thing that happens, which is related to the "precious" outlook, is becoming too focused on one part of the drawing so that it throws off everything else. Maybe that small part of the drawing is what you really want to draw and you should redo your composition.
In life drawing, one small thing being off can ruin it all - if you don't know how to turn the mistake into an asset. So it's really important to develop the entire picture and keep looking at and measuring how all the parts of the scene relate to each other. I usually begin with a line drawing to set up the composition. Sometimes I end up liking the line drawing so much, I'll stop and call it finished. More often, once I get the line drawing done to my satisfaction, I establish where my darks and highlights are, and I try to work as quickly as possible to model the entire picture plane.
Do not listen to the negative self-talk that can happen when you're struggling with something in a drawing - that can steal your motivation. Before you wear that part of the drawing out, get out a sketch book and work on the thing that is troubling you. Keep pushing through the struggle and you'll eventually be victorious and feel really good about your accomplishment. That's how I keep motivated - with constant reminders that if I just stick with it, no matter how painful, I'll elevate my skill to a new level.