You need to place yourself in a position that the object you wish to photograph passes in front of from one side of you to the other.
A good starting setting (not essential or always appropriate, but will help get things started) is to use shutter priority (named Tv on Camera dials). The shutter speed you select will determine how much background blur you get during the pan. The faster the object travels past you, the faster your shutter speed can be and still detect movement in the background. There are other considerations when you select your shutter speed. When shooting propeller aircraft you have to be mindful not to freeze the propeller blades by selecting too fast a shutter speed; equally with vehicles, you don't want to freeze the wheel rotation as either of these make the aircraft / vehicle look stationary. Jet aircraft typically have no give away moving parts visible so you can get away with a slightly faster shutter speed (bearing in mind that you still want background blur)
For focus settings, set your camera to AI Servo (this is what Canon calls it, use the equivalent of your brand) and select a single focal point from your AF system which should be placed to cover the area of the frame you wish to keep sharp while tracking the object. The AI Servo setting will constantly adjust the focus of the moving object.
Metering settings will vary depending on the subject - if it is sunny and the subject has highly reflective surfaces (aircraft canopies etc), using spot metering is a risky option as you could meter off the glinting sun and your camera would expose for that rather than the whole scene, I tend to use partial center weighted metering.
The challenge is to smoothly pan the camera along the path of the object without introducing any conflicting movements which will introduce motion blur in the final image. Improving this is down to technique and practice mostly, although some lenses have 2 mode image stabilisers which stabilise only in the direction across which you are panning (if panning left to right they stabilise for up/down movements and vice versa if panning down to up).
Your posture is quite important to provide a solid base on which to perform the panning movement.
- Your feet should be facing forwards about shoulder distance apart throughout the pan.
- Hold the camera firmly with your shutter hand and the lens hand in a suitable place on the lens like you would hold a rifle.
- Tuck your elbows in rather than having them sticking out either side (this helps avoid upsetting other photographers / spectators by whacking them as you pan).
- Start tracking the object as soon as it comes into view well before you want to start shooting (this allows the AF system to lock on nicely and start predicting the object's distance and allows you to adjust to the speed of the object smoothly) pivoting your upper body at the hips to keep your legs and feet in the same position.
- Fire the shutter when you see the image you want in the view finder and keep tracking smoothly as you do so.
- Keep tracking the item after you have finished taking pictures (which forces you to keep tracking while releasing the shutter).
Tripod / Monopod supported:
You can buy specialised heads to assist with using supports (gimbal heads) but they aren't cheap. I never pan supported as I find it too restrictive in movement, especially when in a crowd of spectators: you will have to move around your tripod as you pan, which a lot of time there just isn't room to do.