I suggest you buy a calligraphy course, so that you can have a systematic and comprehensive understanding. Simply put, calligraphy skills can be roughly divided into several aspects: using a pen, using a meticulous brush, writing ability, brushwork, writing, composition, printing and so on. There are many specific contents in every aspect, which cannot be explained clearly in a few words.
At what stage did you learn calligraphy? What problem do you want to solve? To be specific.