I've been told to put "I" at the last part of the subject, as in "My sister and I walk to school." Is saying "I and my sister walk to school." wrong?
According to Grammar Girl, it's "a rule of politeness" to put yourself last in the list:
Ms. Smith informed my wife and me that she was resigning.
My sister and I went to school.
General Writing and Grammar help concurs, but does not offer any additional authorities on the matter.
The Merriam-Webster Learner's Dictionary offers the same advice: third-person, then second-person, finally first-person pronouns for general usage; mixing up the order is not necessarily rude, but can serve to emphasize the role of the speaker in the action, or as a cue that the speaker is talking informally or is less-educated.
I and my sister is a bit odd, yes. As Hellion explains, usually we're taught to put ourselves last in coordinated lists, so you'd write this instead:
My sister and I walk to school.
In formal speech, you should always put yourself last. And even if you put yourself last in informal speech, it'll sound perfectly natural. So the short answer is always put yourself last.
However, it's very much natural English to write or say it the other way, putting yourself first in the list. Native speakers almost all talk this way (until they're taught not to do so), and there's nothing wrong with doing so in informal speech. But we don't say this:
I and my sister walk to school. (very rare, even in non-standard English)
Instead, we say this:
Me and my sister walk to school. (acceptable in non-standard English)
I want to emphasize something: although this is extremely common, it's a stigmatized speech pattern and should be considered non-standard. You don't ever have to speak this way, but you shouldn't be surprised when you hear other speakers do so.
The issue here, as in the discussion above, is not only about grammar but also about custom and usage, whether "formal" or "informal," whether in writing or in speech, etc. I agree that, per custom and usage, we are taught both to say and to write, for example, "She and I are going...," and not, "I and she are going." However, we are taught that such constructions are necessarily an issue of correct vs. incorrect grammar. I do not think so.
Again, I am in the camp that would always say/write, "She and I...," not "I and she..."; but linguistically/grammatically there is nothing incorrect per se about saying/writing "I and she...."
"I and she are going to the store" (i.e., "we are") conveys the exact same information, perfectly understandable both to speaker/writer and hearer/reader, and employs the correct nominatives "I"/"she" (vs. incorrect objective "me"), but in a different order (I/she instead of She/I) than--agreed!--we are acCUSTOMed to using them.
But custom, etiquette, and grammar/linguistics are different animals, even if they so often overlap that we do not discern their differences. I think this discussion requires that we acknowledge such difference for the purpose of (re-)examining how we construct a sentence--such as "She and I are going to the store"--whether per custom and/or usage and/or linguistics.
That said--ha!--I can't imagine I would ever say/write "I and she...."
You would say "I am going to school" however, to include your sister in the sentence you would say either "I am going to school with my sister" - which is logical, grammatically correct and understandable, also use of I in the first person tense is acceptable in this instance, or My sister and I are going to school. However to say "I and my sister" is incorrect as you are using the wrong "person" tense, "me and my sister" is also wrong, you could scrape by using "myself and my sister" although to be grammatically correct it should be "My sister and I". "I" indicates yourself as "active" i.e. a subject pronoun, I read, I run, I walk, I think therefore I am. Try adding me to any of the aforementioned and it does not make sense. He asked "me" i.e. having something done to you, make me the "object" pronoun.