Hi, clearing the Flash Cache may help too, however I have had this problem in the past, where the meter jerks in small increments.
It is most likely caused by some processes running in the background. I try and only have this game open when playing (close all other programs) , and many recommend to have a dedicated browser just for WGT. You can try using something like Gamebooster or similar - all it does is monitor your PC and what processes are using your resources.
The biggest problem with many computers are the virus scanners, depending on what you use this could well be causing issues.