Liu is Gu, Liu is Liu Gongquan and Yan is Yan Zhenqing. You start with one of them.
Liu Gongquan's shelf structure and basic strokes are very good. I always ask students to start with Liu Gongquan's copybook. I suggest you start with Liu Gongquan's copybook.
Copy, temporarily face the copybook and learn to write. Copy is to cover the copybook with transparent paper to write. I think copying is enough. The key is to read the copybook, understand the strokes, structural features and strokes of the copybook from the heart, and then make rapid progress.
Wish you success!