Well depending on my current Role i react differently to the "new player" notice. If im a tank / healer i usually take more note to those things. But i usually always ask before a fight if everyone knows what to do. If someone has doubts id rather take those 20 sec to fill in on a boss fights core mechanics.

Call it spoon feeding or w/e I dont care, its less of a frustration if people gets a heads up before the fight, even if they didnt fully understand what i meant. You can never expect a first timer to fully comprehend a fight without experiencing it first hand, but it sure helps if they atleast know that some adds shudnt be killed like... bombs in copperbell mines anyone? Too be honest most of the rushing nancies from duty roulette makes this fight a pain in the ass.