IFR Flight on IVAO is relatively simple as long as you follow these basic rules.
In real life you should file a flight plan before starting an IFR flight. There is no altitude limit to fly IFR. IFR means that you fly and navigate to your destination by means of Navigational aids such as VOR beacons, NDB Beacons and Intersections. If your flight commences outside controlled airspace (see airway charts) you do not need clearance to operate, however you must request an information service from an ATC unit and remain outside controlled airspace until cleared to enter.