Coolant Temp: With the engine warmed up...put it back to the same position it normally sits.
Tach: With the engine on at idle, put it back at ~800rpm (assuming your car is idling properly)
Spedo: With the key in the On position...put the needle back at zero
Gas: Under the ash tray cup there is a harness that leads to the gauge sender in the tank. Unplug the harness and ground the pin for the gauge needle. (There are 3 wires...grounding one will cause the warning light to come on, grounding the other will cause the needle to go to Full.) Give it about 60 seconds to reach the full mark..then put the needle back on.
Boost: With the engine off, and the ignition in the On position the needle should be at the +- mark (about 1/4 of the way up)