"Everyone was talking in the pub tonight," said my long-ago boyfriend.
"Really?" I said. "What about?"
"About you and I."
We've all experienced moments like this, when someone close to us comes out with something so frightful that for a moment we find ourselves wondering what we ever saw in them. I used to have a friend who used 'lay' intransitively. Every time she said it, I would feel myself physically cringing.
And yet this confusion of the first person singular pronouns is one of the most common mistakes people make in English speech. I'm not sure it isn't the most common of all. I think it has its roots in early childhood, in second-rate primary schools where second-rate teachers berate children for saying things like 'me and Joe went down the shops'. Cowed but not really understanding, they learn that 'I' is safer than me, and a lifetime habit of cringeworthy statements is born. You see echoes of this kind of thing in today's overuse of 'purchase' and 'utilise' instead of 'buy' and 'use'. To the semi-educated, a longer word is always better than a shorter.
Be that as it may, whatever the cause, using 'I' when it should be 'me' is the easiest mistake of all to overcome. You do not even need to understand the concept of declensions. All you need to do is get rid of Joe.
The thing about Joe is - this is a mistake that only ever occurs in a prase of the form 'Joe and I'. No one says 'Give I the puppy'. Well, perhaps some foreign person just beginning to learn English might, but that isn't what we're talking about. Similarly, you hear things like 'me and Joe went to the pub', but you will never hear 'me went to the pub'. It just doesn't happen. People nearly always get their pronouns right when it's as simple as that.
So, in order to know whether you're using the correct one, all you need to do is get rid of Joe. If you are going to say, for example, 'everyone was talking about Joe and I', try it without Joe. 'Everyone was talking about I'. At once it is obvious. Similarly, you might say 'Me and Joe went to the pub', but you'd never say 'Me went to the pub.'
So that's it. All you ever need to do is get rid of Joe.