Oh, I don't know much about the person you are talking about, but there are too many calligraphy books on the market now, so you often have no choice. But remember one thing, I suggest you practice some regular script with orthodox shelf structure before practicing running script. Recommend the best Copybook for calligraphy: standard calligraphy textbook published by Beijing University of Physical Education (yellow cover), Lin Fei Jing by Zhong Shaojing, and regular script by Gu Zhongan. His running script is also very good and won the praise of experts.
The key is to stick to it, as long as you stick to it for three months, the general characters will be improved obviously (remember that you can only practice one font in these three months, and you must not practice multiple fonts at the same time). But there is still a long way to go to be a family. Ok, that's all, I wish you success ~!