Controlling the plane is by no means easy. If you don’t have a joystick or gamepad, you may not be able to do it at all. Pressing a key to turn is very sensitive, and for the most part sends the plane spinning out of control. You can either work on leveling the plane or work on heading to a destination, not both. In other words, find a gamepad and just do it that way.
If you need help, consult this list of keyboard controls. Spacebar pauses (very important), G retracts the landing gear. Stick to turning with the rudder, not the ailerons, by using SHIFT+the arrow keys. You can also try left-clicking and using mouse controls. I managed to get my speed up to 840 miles per hour and my altitude as high as 41,300 feet. How high can you get it?
Here is a nice video: