My 2000 ford explorer has sat outside in illinois for 16 months what should i do to get it running?

I know it needs a new battery which is the first thing i will do

Drain the fuel tank and replace the fuel filter, add new fuel. Change the oil and start it up. The engine tune will be the same as when you parked it. Your battery may charge up and be fine, if it won't hold a decent charge then replace it.
RETIRED ASE MASTER TECH.
trans fluid might be a good idea… But then coolant and transfer case and differentials are as well.

Give it a tune Up. This means replace spark plugs, Fuel Filter, Air Filter, Drain Gas and Fuel lines, New battery, replace oil and oil filter, drain and replace transmission fluid.