I got a text from a friend, but I'm not sure if it's correct.

Well, let me hear what it is.

Okay, well, at one point, he wrote, I could of gone to New York last weekend, but I don't think that sounds right.

You're correct of is a proposition.

Sentence is missing a verb in this case.

Have it Should be.

I could have gone to New York last weekend.

The confusion comes from the abbreviated form of Could Have That's Could've, which sounds a lot like could off.

I got it and since could is a helping verb, another verb must always follow it.

Not a proposition.

I should write to him and let him know.

Are there any other common mistake that native speakers make?

Well, there's the example of every day vs every day, every day together as one word is an adjective and means comment like every day grammar.

But every day as two words is an adverb praise and describes when or how often something happens.

Every day I go to school, an easy way to remember the difference between every day and every day is that the first is an adjective and comes before and now.

And the second isn't advert phrase and must modify a verb.

And that's every day, not every day, Kraemer.