........If you have the sun behind you, you can often use a much higher shutter speed ... and if you boost the ISO to say, 1000 ... you will be amazed at the flexibility of your shutter speed control..........
The raison d'etre of a shot like this is a slow shutter to give the feeling of movement. A fast shutter freezes everything and panning becomes superfluous.
Judging from the post, I think your technique is pretty sound and you hardly need any tips but here goes anyway.
Stance is clearly important. If you shoot a gun, that's how you want to be. One foot in front, slight crouch, a forward lean and squeeze the trigger.
Shutter between 1/40th (Runner) and 1/200th (speeding car).
Subject has to be in the same part of the frame during the pan, you can't allow it to move across the frame. Again use an AF point like a gunsight.
Go for continuous focus and probably wide area AF or choose a local AF point.
If the shot is repeatable, you can preset the focus point, switch the lens to manual and concentrate on the framing.
You may need to control the DOF with an ND filter (slow shutters lead to be smaller apertures and deeper DOFs).