Generally, I'd recommend starting with the major domestic football leagues in the largest markets because they have the most coverage, the most accessible statistics, and the most consistent quality. You'll find extensive historical data and injury news is widely reported. Smaller leagues are tempting because odds can be better, but the information is harder to find and the quality is less consistent. Pick one or two major leagues and become an expert on them. Learn the teams, the players, the rivalry dynamics, and the seasonal patterns. Depth of knowledge in a specific area beats surface-level knowledge across everything.