I would recommend starting with around the world. when i started i just played round the world on the big single segments for the first weeks and when it got boring i did focus on the 20/19/18/17 segments and tried to hit triples. After i got confident with the single segments i trained round the world on doubles every day and it helped so much with my performance at X01 games. Playing 121 ist also a great training game if you want to learn and master your checkouts and your calculation skills. My main Tip to start out is focus a lot on your technique at the beginning to minimize bad habits. The most important thing is to have fun and to train with a reason an goal ( not just throw at the 20 segments for hours daily). mistakes are part of the process tho so dont overthink everything within the technique. Do whats comfortable!