For a start lots of Research
Tank
Refractometer or Hydrometer
Test Kits (Ammonia, Nitrate, Nirtite, pH, Phos- Salifert are generally considered the best)
Thermometer (Digital are better)
Skimmer
Powerheads/Streams (20x tank volume)
Lighting (Dependant on what coral species you keep)
Liverock
RO Water/Unit (DO NOT USE TAP WATER)
Mixture of Foods
Books
Nets
Salt
5g RO Containers
Water Change Equipment (Buckets, Hose, Spare Powerhead & Heater)
& a lot more Research
I am sure I will think of more items