These are just my tips, so don't take it as gospel...you can always tailor my tips to fit your needs.
Panning is a good way to capture motion...but it's not the only way. Imagine shooting a car coming straight at you. Panning would not work in this situation. Instead, use a very high shutter speed (like 1/1600th or more) and try to get mutliple cars in the pic to capture a snse of "racing". If you're lucky you might even get to capture the heat vapors or smoke trail coming out of a gas car. And onroad cars can also get their wheels in the air during turns. Examples:
I normally shoot from the sitting position. Or I try to find a spot near the track that is lower elevation so that even if I stand up, the camera angle is still very low to the track.
For example, I took this picture while standing:
You might also want to try this right angle device:
I bought one but haven't used it yet.