Give ’em everything and nothing more
Providing just the right amount of information in your microcopy
You’re writing a new screen and you have so much you can say. You can manage expectations for the flow; you can deep dive into value props; you can take the space to build rapport and really express your voice; and so much more. So how do you decide how much to say? How much is so much that they won’t read a thing, and how much is so little that you’ll come off cryptic and leave them more confused than before they started reading?

Everything necessary and nothing else
Give your users the information they need. Don’t leave them stranded or guessing. Concise is not always better and too concise can leave your users in worse shape than had you filled the screen with text. Give them everything they need, even if that means adjusting the design.
But no more than that. If the copy does not offer clear, immediate value, leave it out. (At least for now, more on that later. (Ya see what I did there…))
One thought at a time
When it comes to how much to smoosh into a single sentence, the answer is, a single thought. It’s not as much about the number of characters or words as it is is about messages. Keeping one thought to a sentence usually works. If you’re trying to say too much at once, you’ll lose the user halfway through and they’ll absorb none of it.
If two sentences clutter the screen, consider breaking the experience into two screens. I’ve seen first hand the positive test results of breaking a flow into more screens with less content on each screen, especially on mobile.
Progressive disclosure
You don’t always have to leave messaging out. Sometimes you can include it all, just not all at once. Progressive disclosure can work in two ways:
Chronologically — reveal additional information as the user wades deeper into the experience, adding information one step after the next; or,
Layers — put certain details behind a click (e.g., tooltip, expand/collapse element) so that it’s all there for the user who wants it, while not in the way for users who don’t. The benefit of copy behind a click is that if the user made the effort to get there, they are likely invested enough to read it.
Ask the user
As a UXer this should be obvious, but the best person to ask about how much information to include is the user. Duh.
Talk to your support, sales, and other user-facing teammates. What are users asking? And what’s obvious to them? Maybe you’re wasting precious real estate on information that is industry standard and while you thought you were providing education you are really wasting everybody’s time. Take that out. Dig into support tickets to see the questions you’re not preempting and put that content in.
Limitations
Pay attention to factors that have nothing to do with the copy or the user, but that do affect the experience. For example, what does your copy look like on an old crappy smartphone with a tiny screen? Despite everything we’ve said so far, if those screens can’t accommodate what you’ve written, you probably need to rethink it.
Have more tips? Share ’em in the comments!