Remember that you might lose your payed rank in a wipe. Happened to me once.

Tip: build house, and also throw rock at zombies (if they're bullies), and also also don't build near spawn--

Ask me how I know, or wait I'll tell you, so I built my house and then a zillion-bajillion people came over and kept passing through griefing my house :/

I put signs up and they mostly stopped though (mostly... they stole my sheeps again....)

The rules (PvP, grief/prank, land/feature claim, redstone, 'farming', etc)
the fee schedule (includes 'recommended' contributions / how often – and for how much – the hat gets passed etc)
what mods etc are in use (and what one is permitted to so client side)
the point of the server ("build massive intricate sculptures" and "engage in clan wars" may not be compatible)

probably knowing how to craft wooden tools, knowing server rules, not knowing to dig straight down, how to type in the chat, that kind of stuff,