Learn to sketch fast. Doesn't matters if you correct with resize tool or use different colors. Learn what works for you so your sketch is good(movement, pose, sillouetthe)
Improve your lineart(the faster you get a good line the faster you finish the high quality lineart). There are tools that smoothen lines a bit(I use the smoothen option of photoshop's brush)
Don't waste time coloring(notice how Ina basically uses the color bucket tool for her colors)
Get good refernces.
And just keep drawing and improving all the time. Don't settle for an artsyle that's endearing but flawed. Keep improving. Don't be complacent. Work in your flaws like an autist and try to apply studies to your work. Get material. Buy or pirate art books. Trace for studying then steal those techniques. Steal everything then regurgitate it again and again until it becomes yours and it becomes yours fast.
Tutorials, workflows, good tools, all of them improve your speed and quality. It's all out there. Just do it.