My own pet peeve is the use of "hard" in place of "difficult". Whilst not been strictly incorrect "difficult" refers to a problem or challenge whilst "hard" refers more to an object. Yes I know there is a common usage for "hard" being used for a problem but its a pet peeve of mine and just grates on me every time I hear it (which is often). Over-use intensifiers are similar in that they are not incorrect, but just lazy speech.
One of my favourite reads, when I was young, was Usage and Abusage by Eric Partridge (have two copies of it), which probably says it all
But see the more interesting one's at https://lifehacker.com/are-you-making-these-common-grammatical-mistakes-1836969914
#grammar Are You Making These Common Grammatical Mistakes?
No one can recognize our relentless misuse of the English language quite like an editor. Misplace a modifier, and your editor will (hopefully) let you know. Over-use intensifiers such as “very,” “just,” and “really,” and your editor will tell you that you’re really just not doing your writing any favors. My editor here at Lifehacker has officially broken me of the overuse of “oftentimes,” which, as she pointed out, isn’t exactly wrong, but is just a longer way of saying “often.”