Like any other area you want to learn you should go in with a goal that gives you some intrinsic motivation. At this point in history, Systems Programming is too broad for one person to ingest. Do you want to work on networking? Filesystems? Databases? If you want to get into networking for example (my area) I would recommend you just skip ahead and try to learn ebpf (which is clearly taking over, as Windows has now implemented it). If your interests are other, really do some up front research into what you should be learning.