It depends on whether "my friends and __" is functioning as a subject or an object. If it's the subject you use "I", if it's an object you use "me". For example:
"My friends and I are going out to dinner."
In this case "my friends and I" are the subject, and so you use the subject pronoun "I" (sort of like how "ich" is the nominative pronoun in German.) If it was only you going somewhere, you'd say "I'm going to the restaurant"; if you're going with your friends, you just add them in at the beginning and change the verb to the plural form.
"They're coming to dinner with my friends and me."
In this case, the phrase is functioning as an object, so you use "me" (it's like "mich" or "mir" in German.) And like in the previous example, just remember that you'd say "They're coming to dinner with me." If your friends are going to be there to, just add them in; the pronoun that you use to refer to yourself stays the same.
So, if you ever see the word "me" being used as the subject of a sentence, it's a mistake. ^_^