The examples you give are certainly not "rules", otherwise nobody would ever make a negative statement. I wouldn't even say they were all "principles" either, as they might not all apply in every situation
There are some general principles of writing that we refer to as "rules of thumb". That is an expression we use to describe any broadly true principle which may not be written theory. However, there are so many different styles of writing in any language, and "principles" or "rules of thumb" may apply only to one particular style. For example, journalists often have to stick to "style guides" which may include things like "always write numbers as a word", or "always write 'per cent', not 'percent'". These are not rules outside of journalism.
I did a bit of Googling and I seemed to find the kind of articles you are looking for by using the word "tips". A "tip" is a useful hint which can help achieve a positive outcome but is not necessarily a "rule". One of your cited examples of "prefer positive statements" might be a good tip if you were writing a CV or a resume when you want the reader to think in positive terms.