there is a simple advice on what to do with dungeons you don't know, be it low level or lvl 50 dungeons: Tell the party right away and ask them to explain things to you. In most cases they will, and if they don't, they can't blame you for not knowing the mechanics. Usually i also said it when it was my second or third time in a dungeon and asked them to tell me if i do something wrong. By then i was usually confident enough about knowing what to do.

Now, when it's about the hard and extreme mode primal fights, it's best to read/watch a guide beforehand, as well as tell the party, but mention that you read/watched some guide. The guides give you a good idea on what to expect, but nothing beats the actual experience.