Blowing up from a thumbnail:

• Establish/solidify the viewpoint.
• If you're losing lines, start a new layer or mark the correct line with another color.
• Adjust vectors- keep evaluating.
  
• Flip horizontal
• Stay with feeling, provided the construction is happening along with/underneath. If it's necessary to work something out and go formal, dip in only as long as is necessary to figure out the problem and get back to feeling.
• Find lines of action
• Thumbnails that are too geometric might not translate especially well. It may take some extra finagling to find your way, and it might be a struggle to inject the feeling afterwards. Don't be afraid to change, but even a geometric thumbnail has some original feeling you need to preserve.
  
• Mind your inter-character vectors when thinking about construction & lines of action.
• Draw the more important vectors in, even if they're invisible.
• Watch for happy accidents.
• Don't think it through if you can feel it through.
• Is there a better line of action?
• Don't be precious, unless it's about preserving your original feeling.
• Scribble down your idea. Flesh it out later. Again, watch for happy accidents.
• Stop to relax.
• If you end up making lots of corrections when flipping horizontal, don't be afraid to start the next layer using the flipped version- especially if the other side is saturated enough with marks that you can't see the corrections through the layers.
• Act out the pose if necessary.
• Recognizing what's off is sometimes better than trying use your brain to analyze or plan it out.
• Different characters/parts in different colors can help- especially when there's overlap and you need to draw through another character without losing lines.