For LA should you comment on the writer/speaker's credibility? I've read that you should but I've been marked down for it in the past.
Also, in expository essays is it okay to refer to real examples in a general manner? Again, I've been marked down for not referring to and quoting specific articles written about events because making more general references to events appears less 'researched' and more derived from general knowledge.
Yes, always a good idea to discuss credibility and authority, especially when there's a byline like 'Professor Lee is a .... at ...' etc. Discuss how the credibility is used and how it makes readers or listeners more likely to warm to the argument, and also what they're likely to think and feel.
Yes, ALL examples in your expository should have quotes and evidence to support (bar personal anecdotes obviously). You should have at least 3 or 4 quotes to support examples. Know a few good movies and songs so that you can use these in the exam - the quotes will be extremely easy to memorise obviously. But don't write on too many songs and movies, I would suggest talking about 3 examples from the text, plus 1 song, 1 movie and 1 historical event.
Many English teachers are also History and Humanities teachers, so if you discussed Stolen Generations as an example without quotes, they wouldn't be too happy. No quotes also make the essay seem less reliable & examiners will be less likely to 'believe' what you're saying. For this reason, I steer clear of personal anecdotes since they are (1) corny and (2) not as believable. Good luck!