Yes Soup I didn't explain myself properly. So to my ears John and I sounds fine, and me and John sounds fine.
two different problems here. One of them is whether to use I/me, and the other is whether John should come first or second in the pairing.
The first one is, as everyone has explained, easily worked out by deciding which one you'd use alone. "I was cooking" - yes, so "John and I were cooking". (You do have to change the verb to match sing/plural, but that's irrelevant to working out whether it is I/me). "He cooked for me" - yes, so "He cooked for John and me". This is a grammatical issue, and one where there is a generally accepted right and wrong answer.
The second issue is which one comes first. This is not so much a grammar issue, as a stylistic one. It is not actually wrong to say "I and John were cooking" - it just sounds a bit odd. To make the sentence flow, or for the sake of politeness, it is more common to put the other person first, and "I" second. But sounding odd doesn't mean that "I and John" can't be used, though it would be more common if you were trying to emphasise the "I" (and likely would be puncutated with dashes or the like in the order to show that: "I - and John, of course - cooked this amazing meal for you")
The misuse of "myself" and "yourself" also bothers me, because I know the other person is trying hard to sound posh or educated, and yet is coming out as the opposite, and it makes me cringe for them because I know that I get embarrassed when I say a word wrong that other people know how to pronounce or use an expression incorrectly, and I think that they will be just as embarrassed if they find that they've been doing this. I'm not sure that actually happens though!
The most common use of "myself" is just to emphasise that it's you that are the subject or object of the action - "I made it myself" or "I hurt myself"; it doesn't really indicate formality or politeness (don't need "my husband and myself" or "please return the form to ourselves", etc). I know that some people have been told not to use "me" (because they should be using "I", as in the "John and me are cooking tonight" examples), but then they hypercorrect this either to using "I" all the time, even when wrong ("He cooked for John and I") or to using "myself" all the time, even when wrong ("John and myself were cooking" or "He cooked for John and myself").