The best thing a beginner having problems with high speed taxi can do is to find someone with an R/C car or boat and practice fast runs back and forth in front of you. It's actually best if you can find someone with a stick radio rather than a wheel. A bonus is if they can put steering and throttle on the left stick since that's the one used for most planes to handle the ground steering. This lets you practice your orientation while removing the fear of having the plane takeoff. When you are comfortable with the land/water vehicle, do the same on the plane. Rather than always rushing to get the thing in the air, spend some time practicing the ground handling.