I find it interesting to observe the changes in grammar, punctuation and pronunciation which have occurred in my lifetime, currently spanning 60+ years.
Here in Australia and I believe in most western countries, big changes in education occurred in the 1960s which led to what I view as a change in standards. The statement was made that these rules were not necessary so long as everybody was able to understand what was meant. Fair enough but my observation is that ambiguity is far more prevalent than it used to be and far more misunderstandings occur as people don't know the meaning of words.
Maybe I'm looking at it with rose-tinted glasses but on this last point, I remember we used to have a subject titled just that, 'The Meaning of Words". Everyday we took home a list of ten words with their meanings and and we had to know them when we were examined the next school day; no comments about "murdering trees" came from our lips because we knew the word "murder" referred to killing a human being. It would appear a lot of people don't know that today.
The rules of pronunciation were well known. I bet if you ask anybody under fifty what the vowel, consonant, vowel (VCV) rule is, they would stare at you blankly as they were never taught it. Stated simply, when you have three letters in a row in that form, the first vowel is pronounced by its name not its usual sound. Hence the change in pronunciation of words such as status, project, menu, leverage (lever), premier, venue, data, etc.
Making nouns plural is another area of change. A common lack of understanding is for words ending in "f" and "fe". Thus the plural of knife is knives; roof, rooves; wife, wives; elf, elves; wharf, wharves and wolf, wolves. Then there are the words which we learnt didn't have a plural. These words are by their nature a description of a class or a heading for which there are various types and as such are unique. When something is unique, it means that there is only one of them and so by definition it cannot have a plural. Examples of such words are sport, fruit, meat, cheese, art, craft, wine, etc. Thus for us "sports" didn't exist; we had to express it as types of sport; types of fruit; etc. It was interesting to note how the Nine Network used to talk about "Wide World of Sport" but at sometime (I don't know when) they changed to "Wide World of Sports".
Grammar has seen the biggest change with the incorrect use of "who" for "which" now almost universal. "Who" used to only be used when referring to a human being and a word such as team is an intangible noun and is not human even though it is composed of humans. It seems that the concept of the intangible noun not being human is almost unknown. "The dog who chased the ball" still feels terribly wrong to me. "The dog which chased the ball" feels much better. To put an unscientific number on it, I think something like 80% of the times "who" is used, it is done so "incorrectly".
When I was at school we well knew the words which couldn't start a sentence. They were and, but, also, or and nor. Logically this rule should still apply because by definition they require something in front of them but I continually see them starting sentences in newspapers, magazines and of course on the internet.
This same group of words leads me to the common punctuation "mistake", i.e. the misplacement of the comma especially with the listing of adjectives and nouns. In the example "the balloon colours were red, green, blue, yellow and black" there is no comma before the "and". We learnt that there were a number of seperators which could be used for this sort of situation. These were the comma, the semi-colon plus the words and, but, also, or and nor. All of these items were of equal standing and so to place two of them together (e.g. , and) was just silly. We also learned that if placing a breath comma with those words, it was placed after them so more emphasis was placed on the following words.
The decision of the Americans in the 1940s and 1950s to standardise their version of English has also caused more confusion, especially since the arrival of the internet. Their decision to eliminate "ou" in favour of "o" in words like colour; the elimination of "ph" for "f" in words like sulphur; the use of "er" for "re" in words like centre; the use of "ize" for "ise" in words like standardise and the elimination of double letters in words like Nanna and labelling has caused a lot of confusion and has even changed some pronunciations. I don't care what they say, "z" is a "zed" not a "zee" - blame Sesame Street!
Spelling has always been a problem but the kids no longer seem to know the simple little sayings we had to help us, e.g. "i" before "e" except after "c". What now seems like a common occurrence viz., the splitting of single words into two words, has increased dramatically, e.g. road work for roadwork; all ready for already; all right for alright; any time for anytime; in to for into (the same with onto); with in for within; how ever for however and I've even seen sand shoe for sandshoe.
These are a few of the things I've observed and provide examples of how language is a living thing, constantly evolving and changing. Of course I don't know where it will go next but personally I would like to see some of the old "rules" brought back although I doubt that will happen.