When the regular script reaches a certain stage (that is, the structure is basically fine and the punctuation is basically fine), it is necessary to practice the running script. If you don't practice running script, regular script will be rigid and can't be opened. As for the choice of running script copybook, if you are practicing European style or Liu style, you can choose the Preface to the Holy Teaching as an introductory copybook, or you can choose Wen Zhiming's Preface to Red Wall Fu Tengwang Pavilion, or Ou Yangxun's Post to Hans as an introductory copybook. Those who study Yan style can directly choose Yan Zhenqing's manuscript of Sacrificing a Nephew as a beginner. These running script copybooks are characterized by their combination with Fiona Fang. When you have a certain running script foundation, you can learn Zhao Mengfu's running script, such as Fu on the Red Wall and Fu on Autumn. But while practicing running script, don't abandon regular script. Regular script and running script should be practiced together.
In the cursive stage, we can start with Sun's Book Score, which is not only a model of cursive learning, but also a classic book on learning books from ancient times to the present. You can also learn from Zhi Yong's Thousand Characters. When we have a certain foundation, we should trace back to the demeanor of the two kings in Wei and Jin Dynasties. We should study Wang Xizhi's cursive scripts such as Seventeen Sticks and Duck Head Pills.
The above is my experience in learning books, which is the general route of learning books. With this foundation, I visited various families according to my own preferences, such as Song, Huang, Yuan Xian, Dong Qichang, and Qingcheng Tieweng Liu. I wish you success! Hope to adopt.