Kick out dead weight
The default loadout for each aircraft is a passenger in every seat and fully loaded baggage compartments. Kick some of this dead weight out to make your plane lighter and more responsive, and to get more mileage from your fuel.
Navigation
To learn the art of navigation without relying on GPS, start with a short flight between two nearby airports and concentrate on learning the VOR and DME equipment. Then plan longer flights with multiple waypoints.
Tune your radio
Open the Vector Map (Shift-M) to get an overhead view of your position. Click on airports and navaids to bring up their info boxes, then click on the radio frequencies in the box to automatically tune your radio.