What can you do to a 1990 2.9L V6 Ford Ranger XLT 2WD standard to improve fuel economy or power output?

You can start with a set of spark plugs Change the plug wires and Distributor cap and rotor. new air, fuel filter, pcv valve, Check timing and change your oil. that should help with some fuel economy and power if you are looking for morepower then you will have to look for a power chip or a programmer for it.