We taxi out for an instrument flight just as we would VFR, making calls on CTAF or obtaining a taxi clearance, as appropriate for the departure airport.
In addition to our normal taxi routine, we will need to verify our instruments check out okay for IFR flight. On the taxi out, the airspeed indicator should show zero. The attitude indicator should show level. It's horizon bar should stabilize within 5 minutes and should not drop more than 5 degrees during taxi turns. The altimeter should show field elevation within 75 feet. The VSI should show zero. If the VSI does not show zero, this is still okay. Just note this indication and use it as the zero indication in flight.
The operation of the directional gyro and turn coordinator can be verified by making slight turns left and right on the taxiway. Both instruments should show the turns correctly. The directional gyro should indicate your proper heading on the taxiway, and your turn coordinator should not show a flag. The inclinometer should be full of fluid and contain no air bubbles. The ball of the inclinometer should rest in the center mark when level and not turning during taxi. While turning it should be thrown to the outside of the turn, moving opposite the direction of turn. The heading indicator should be checked against the compass again before takeoff to ensure it has not drifted during taxi.
Other than this instrument check, taxi out, runup, and departure are the same as they would be for a VFR flight.
Following Taxi Instructions
Before any flight, the airport diagrams for airports to be used should be studied by the pilot. By studying these diagrams and going along anticipated taxi routes in your mind, you can avoid confusion when it comes time to actually taxi the airplane.
In an attempt to reduce the odds of a runway incursion, air traffic control will issue an explicit clearance for all runway crossings. The controller will very clearly state "cross" or "hold short" for each runway you encounter along your taxi route. Air traffic control will not use the word "cleared" when issuing taxi clearances to avoid confusion.
The tower may need you to hold short of the approach hold line or ILS hold line. In either case, the controller will state this clearly. For example, "Cessna seven zero eight golf lima, hold short runway one seven right approach" or "hold short of runway one seven right ILS critical area".
The pilot should read back the taxi instructions, including the runway assignment and any instruction to hold short or cross a runway.
If at any time you become disoriented on the airport, make sure you are clear of all runways, then stop the airplane and inform the controller immediately. They will want to sort out any confusion just as badly as you do, and making sure they know where all aircraft are on the airport is their first priority. This is especially important in times of low visibility, when the tower controller is unable to verify aircraft compliance visually.
Some airports have installed the Surface Movement Guidance and Control System, or SMGCS, pronounced "smigs". These systems aid aircrew and vehicle operators move on the airport surface during very low visibility. They incorporate additional lighting, markings, and air traffic control procedures. These systems should not affect general aviation operations. But, if you see something that confuses you, just ask air traffic control.
As always, focus on the taxi route. Hold checklists and nonessential communication until the airplane is stopped. Otherwise, you open yourself up to distraction, which could lead to a mistake. You want to avoid crossing a runway without a clearance, turning the wrong way on a taxiway, departing on the wrong runway, or departing from an intersection instead of full length by mistake. These mistakes can all be made from doing something that might seem quite harmless, such as having a discussion with a passenger at an airport you are very familiar with.