It's not the best practice, but sometimes I'll just draw a part and "solve" a thing based on what's already down. Everyone has their own way of doing this, but I'll share mine. 
The thing's got a pretty strong vector to it [as indicated by the black arrows]. I also made a couple connection points [you could call them bridges -- red arrows]. My next move will make use of these things. 
What I drew in initially, I noticed, included an overabundance of round forms, so I experimented with angling them a bit more, for the sake of sharpness/variation. 
Had I been using my noggin a bit more, my next move would have been something notably SMALLER or notably LARGER than the mouth....but we'll continue working with what we've got. 
For the body, I swing hard to port -- REVERSE VECTOR. 
For the gills/fin, I cue off the pre-existing vector set up in the droopy eyeball. It's there. Might as well use it. 
Notice how the flow starts to cut in the other direction. Nothing constant. An alternating wave. 
I add a few bits to "swift it up", but my next choice is predictable. A fish chasing another fish. It's at least a MUCH SMALLER fish, but is this the best "move" I could have made? 
Why not a scuba diver? [Quick answer : Didn't want to stop and look up ref.] 
....or why not this? A role reversal? 
The "next move" is so exciting when you weren't aware of it 30 seconds ago. What's a surprise to you will likely be a surprise to the person who sees it. 
We tend to stick to drawing things we KNOW we can make look good. We don't WANT to show a thing in a new context, because we don't know how to convincingly draw that stuff. We suspect it won't "come off." 
Or...and this is often the case....that new context involves *too large a departure from what we've already drawn.* We'd have to start all over again. Iteration 2. This is what's required, unless you go the other way. Clairvoyance. Forethought. 
Our idols all have a mix of vision and improvisation. They have the ability to formulate ideas in their minds before any marks are made (the moves BEFORE the moves), and the ability to bullshit:) Theirs is a process of creation AND discovery. What will your next move be? 
