1) Don't make jokes about their difference from you. This means, if they have a different skin tone, don't make jokes about it. If they have a different gender identity, don't make jokes about it. (this includes "jokingly" or "affectionately" using slurs that refer to a group you're not in) If they have a different relationship style, don't make jokes about it. There are many reasons for this, but the very most basic is that it feels like you're saying "you're not one of us, isn't that funny?"
2) Don't make general statements about how "those people" who are different from you behave, look, think, etc. If you are not one of that group, you're probably just repeating stereotypes, so just don't make general statements. NO, knowing someone from that group -- even very very well -- DOES NOT change this. If you're quoting someone else's opinion on group A, make sure that person is a member of group A and make sure you state it as a quote of a specific person, not as a general fact.
3) Don't make assumptions, and don't put the burden of your ignorance on other people. If you don't know, educate yourself through the internet and the library/bookstore. Feel free to ask for resources, but don't demand free tutoring. You can ask IF the person WANTS to be extremely generous and give you free tutoring, but there is a reason we pay teachers, professors, and tutors -- it's WORK teaching someone, highly skilled and frustrating work.