Some of the most common complaints about “bad writing,” which is an overly generic term itself, is that the writing is flat, lack luster, soulless, drab, unoriginal, insert more synonyms for “boring” here. I've heard through the academic grapevine (i.e., Rachel Toor's article in The Chronicle of Higher Education blog) that some writers have literally been rejected from journals because the writing is “one-dimensional and dull” and “lacks soul.”
What does it mean when your writing “lacks soul?”
It means that you are holding yourself back, unwilling to portray either your own humanity or the humanity of the people you're writing about.
For non-fiction writers, I get it. I've been there. In order to be well-received in a peer-reviewed community, you feel the need to hold yourself outside, as an objective, impartial observer. You're worried that if you focus too much on your subjects/participants as people with feelings, emotions, troubles, and hopes, that you will not sound like a third-party observer and, so, will not be taken seriously. And if you talk about your own troubles and hopes, you'll be shoved into the memoir category. Heaven forbid.
Whether your peer reviewers want to admit it or not, they are humans.
In the sciences, in particular, we have a standard of remaining distant that we tout, but, when push comes to shove, we are still human. There exists a tension inside of us. We want to remain impartial scientists, but our humanity loves a good, empathetic story.
Even if the editor of a publishing house doesn't want to admit it, s/he is swayed by emotions, if only a very small sway, but that small sway may be what gets your article into the slim, “keep” pile or thrown into the large “reject” pile.
Start with three small steps to put soul (humanity) into your writing.
1. If you're suggesting a broad theory of human behavior, provide some examples that are highly relatable.
For instance, if you're doing marketing research on which consumers might make quick, emotional decisions and which consumers might make slower, rational decisions, give us an elaborate example! Paint the setting, give us two shoppers in a super market or a mall, tell us what the scene looks like, what kinds of people these are, how they're dressed, what products they are looking at, what factors go into which product they choose. Make up a bunch of details. Yeah, the details might not be entirely empirical, but you can qualify that. (You can qualify anything!) Make us care about these two types of consumers and the decisions they make.
2. At the end of a piece, you might give a short explanation of why you care about the research you have just explained.
I recommend doing this at the end of the piece because some non-fiction readers will be turned off, just on principle, by you talking about yourself in a “serious” piece. But, once you've presented all of your research and findings, giving a bit of your own humanity will leave the reader with a sense of connection, and that connection will leave a positive emotion as they set down your piece. The reader will feel like s/he understands your motives and research, and we always feel more positive when we understand things.
3. Don't be afraid to use “I.”
Seriously, it is just fine and dandy to use the “I” and “we” pronouns, even in the most serious and prestigious of non-fiction writing. See Helen Sword's (2012) extensive qualitative analysis of academic journals. By merely saying, “I conducted this researching using such-and-such methods,” you are drawing the reader in closer, inviting the reader into the research process. We love to be invited in.
Remember, writing is just one human talking to another human about human types of things.