Need help with OBD codes and where to start?

I have a 93 cadillac deville the OBD says the following code errors:
E26 - Shorted Throttle Signal Switch
E31 - Shorted MAP Sensor
E48 - Exhaust Gas Recirculation Sysyem Problem
E52 - PCM Memory Reset
E55 - Closed Throttle Angle Out Of Range
E75 - Intermettent VSS Signal
E91 - PRNDL Switch Problem (transaxel range switch problem)
E98 - High RPM P/N to D/R Shift

Which problems should I tackle first? How do I know where to start with all of this?