In Chinese calligraphy, the way the brush is held is very important. You cannot afford to hold it any old way.
As a long speech is not worth a good diagram, here is the usual way to hold the brush in Chinese calligraphy:
To write very small characters, the wrist is placed on the table. For characters of average size, in an imaginary square of 5 to 10 cm on each side, the other hand should be placed under the wrist.
For larger characters, the forearm rests on the edge of the table.
To make large characters in the Grass style, you must stand up and hold the brush by its top as shown in the diagram below.
For the largest characters (called Bangshu), a large brush is used and held in the following way:
To write vertically, on a wall for example, the brush is held in this way:
Apart from the last case, the brush must always remain vertical.