As a scientist, you owe it to your work to tell the story it confides in you. Data is what data is, but as a writer it is your job to make it a story worth telling. As a scientist and a novelist, I write both facts and fantasies. Through comparing the processes though, I was surprised by the number of similarities.
Characters: In order to write both science and fiction, you need to understand your characters. My thesis had a whole host of characters. The main one was called Prospero, a tumour suppressor I became intimately acquainted with over four years. He is possibly the most complex character I may ever have to write about.
Language: The language used when writing science or writing fiction is possibly the biggest difference between the two. Misinterpretations hurt science so data must be described so all readers comprehend the same. Whilst novelists might use any number of descriptions, science is often more limited. Yet although science must be written accurately, it can still be beautiful. The prose less purple. The metaphors non-existent. Nonetheless, good writing has rhythm, flow and pacing; no matter the subject.
Audience: Ironically, those reading science by day often read fiction by night. The approach when picking up the manuscripts are opposite though. As scientists, we are taught to be critical, yet when reading a novel we look to be entertained, suspending our disbelief out of a desire to be convinced by another reality.
Writing: Crafting any manuscript takes time. Science or otherwise, the road to publication requires commitment. Writing science can be slower though since everything must be researched and referenced. A 750 words an hour standard can be reduced to a 4 hour slog. All manuscripts must be revised more times than the author can stand, with carefully crafted passages being cut to aid flow or word count targets.
Ending: Both manuscripts might have a final full stop, but the expectations upon reaching each ending are very different. In a novel, the reader expects an ending, one where all loose threads are tied in a neat bow. Science is never so finite though. We work upon the spectrum of discovery and an ending implies there is nothing left to learn. So it is we leave our endings open, inspiring questions rather than closing them off.