Do you usually sit or stand when writing Wang Xizhi's running script?

Sitting or standing posture is not important. Because Wang Xizhi and others generally don't write standing up.

The important thing is whether to hang your wrist or not. Wang Xizhi, who was sitting at that time, had a short desk, so when they were writing, their elbows and wrists were suspended.

To learn calligraphy, unless you are very young, it is recommended to hang your wrist and practice, and the table should not be too high. Standing is ok, but according to the height of modern tables, hunching is inevitable. Of course, it is best to stand when writing big characters or creating an entire article, so as to grasp the overall situation. If you practice calligraphy at ordinary times, it won't be too big. There is no need to stand.