The best thing to do is teach them the basics. How to action in /me, the difference between normal roleplay chat and LOOC, /y, /w etc. Once players have that down it solves a lot more failrp problems and gives them a good head start to roleplaying.
You can’t really show people how to roleplay, detailrp is more of a social standard than anything. You show players the mechanics of the game and allow their creative liberty run wild when they create their characters and make friends. Instead of shaping new players into how YOU want them to act, allow them to choose what they want to do with proper guidance.
That said, be willing to answer any questions they may have, and if they need additional guidance on what they can and can’t do you can point them towards the server and terminology rules.
Please remember, a good roleplayer isn’t one that focuses solely on the amount of detail put into every acton. What makes a good roleplayer is a stand up member of the community that can both write a good story for themselves as well as lead by example and offer assistance to those who ask for it. That’s just my opinion though :)