Quarantine everything wet - corals, inverts, rock, sand, fish.....
Anything wet can bring/transport pathogens.
For corals, inverts, rock & sand - simply keep in a separate tank for a minimum of 4 - 6 weeks without any fish in that tank. Parasites need a fish to continue its life cycle - no fish and the parasites will die off.
Do not add any new specimens to the QT while you are quarantining.
While your inverts, corals and rock are in QT, you can watch for unwanted pests - crabs, aptasia, red bugs, etc and treat.