Most advice about plain English is either too vague to act on ("be concise") or a list of words to avoid with no account of why. What actually helps is recognising the small number of shapes that make writing heavy, because once you can see the shape you can fix it anywhere it appears.
There are about six of them.
Phrases that are doing the work of one word
English has a set of stock phrases that expand a single conjunction or verb into four or five words. They feel formal. They are just longer.
- in order to becomes to
- due to the fact that becomes because
- in the event that becomes if
- in spite of the fact that becomes although
- at this point in time becomes now
- a large number of becomes many
- is able to becomes can
Notice that every replacement is a word most people would use out loud. That is the test: if you would not say it to a colleague, it is probably one of these.
Verbs hiding inside nouns
A verb gets turned into a noun, and then a weak verb has to be added to carry it.
- make a decision becomes decide
- give consideration to becomes consider
The original sentence still has the action in it, but the action is no longer the verb. Putting it back is almost always shorter and always clearer.
Latin where Germanic will do
English usually offers two words for the same thing, one from Latin and one from Old English. The Latin one sounds more official and is harder to read.
- subsequently becomes then, or later
- prior to becomes before
- numerous becomes many
- commence becomes start
- terminate becomes end
- endeavor becomes try
- ascertain becomes find out
- utilize becomes use
- leverage becomes use
That last pair is worth pausing on. "Leverage" as a verb almost never carries meaning that "use" does not.
Pairs where one word already contains the other
- past history becomes history, because history is already past
- future plans becomes plans, because plans are already future
- close proximity becomes proximity
- each and every becomes each
These survive because they sound emphatic. They are not; they are just redundant.
Intensifiers on absolute words
Some adjectives have no degrees. A thing is either unique or it is not.
- very unique becomes unique
- absolutely essential becomes essential
- really quite good becomes good
An intensifier on an absolute adjective weakens it, because it implies the word alone was not enough.
Negatives that describe the positive
- not unlike becomes like
- not infrequently becomes often
Double negatives make the reader do arithmetic before they get to the meaning.
Two structural fixes
Passive voice is not wrong, but it hides who acted. "The report was written by the team" becomes "the team wrote the report", and the sentence gets shorter as a side effect. Use the passive deliberately, when the actor genuinely does not matter.
And run-on sentences joined by "and" are usually two sentences. Splitting them costs nothing and the reader stops having to hold both halves at once.
Why this list is short on purpose
You do not need fifty rules. You need to recognise six shapes: a stock phrase doing one word's work, a verb trapped in a noun, a Latin word where a Germanic one fits, a redundant pair, an intensifier on an absolute, and a negative describing a positive. Everything above is an instance of one of those.
If you would rather have the pass done for you while you concentrate on the argument, the BeLikeNative writing assistant applies this kind of edit as you write.