Other than shortening sentences, inserting lists, and using document structure, there are a couple of "easy edits" that I make to most documents that other send to me for review:
- Remove all first person, both singular and plural.
2. Remove all passive sentences, typically by making the sentences more imperative.
In practice these changes are often related.
Expunge the First Person
Removing the first person is important less because it's "more formal" to avoid the first person and more because it's always unclear in documentation: Who are "we," and who is "I"? Should I read "I" as "me" or as the author of the documentation? What if my experiences and environment isn't like "ours?" While we can resolve these confusion points pretty quickly it gives users another set of information that they must track. And given that technical subjects can be difficult without confusing language, there's no reason to make things more confusing.
People tend to think that this makes their documentation "friendlier," "personable," or "intimate." People used to interacting directly with users (i.e. people doing user support) are particularly susceptible to first person problems. In support cases, that little bit of personal touch is incredibly valuable and goes a long way toward making people feel comfortable.
Those people are wrong. Don't do it. Speak simply. Write about the product and the processes you're documenting, not yourself. Convey facts, not opinions. Provide context, not perspective. If you're writing the official documentation for a product, your perspective is obvious to readers; if you're not writing the official documentation, that's also apparent and probably not your job to disclaim.
Use Good Verbs
Passive sentences and weak verbs are a huge problem. Huge. People with science and engineering back rounds seem to prefer passive sentences because they think that passive sentences convey objectivity, and that this objectivity is desirable.
Passive sentences do convey a sense of objectivity, and there are some cases where there's no way to avoid describing a property of a thing except passively. That doesn't make the passive voice generally acceptable. Related to the reason above, passive voice tends to provide a level of "syntatic indirection," and means that complicated sentences become unnecessarily difficult to comprehend.
In documentation, unlike some other forms, it's possible (and desirable!) to use imperative verbs, which provides some relief. One of the main projects of documentation is to inculcate "best practices" (i.e. values and conventions,) in users. Imperative verbs are great for this purpose.
In short: Do it!