Grid and Schedule
Don't be lazy, spend time in every area of the image
Steve Huston recently left a tip on Instagram that read something like: Complete every portion fully enough to be cropped and framed as a piece of finished artwork on it's own.
You've long been wanting to do a study of one of your favourite artist's work. You want to answer the question: "can I complete a world-class image in my own style?" The answer is yes. The only thing standing in your way is laziness.
Grid out your current piece and work on one section at a time until the entire thing is complete.
Spend time, execute intention.
Execute intention in each area so that any area could be a cropped piece of artwork on its own. Not necessarily rendered, because some areas will have less detail than others, but intention needs to be executed in each area. Make icons recognizable, nothing should just be scribbled in. Every object in the image must be recognizable, just as every sentence in a story must be necessary.
Consistent level of finish throughout the piece. Finish only to the level that you're excited about.
This is why artists say to "keep moving around the image as you work". So that you don't get stuck bringing one part of the image up to a level of finish that you either:
A. aren't interested in bringing to the rest of the piece, therefore leaving the rest of the piece looking unfinished or
B. don't have time to bring to the rest of the image. You've experienced situations where matching the level of finish you established in one area forces the rest of the image to take weeks to match.
Above is a Kyle T. Webster image with a simple but effective finish.
The level of finish that you bring to your work is crucial to pay attention to. Not all artists bring their level of finish up to photorealism. Whatever your level of finish is, make sure that it's consistent in all areas of the work.