Most drivers started go-karting (not the electric one like K1) when they're like 8 years old or so...then move on to junior formula series (like SV in Formula BMW), then keep advancing in various series and finally GP2 or become test drivers/reserve drivers for F1 teams. But most important of all, make sure you shine in those junior series because many scouts are watching.
To win a championship, you need to be in a big team, consistent car, you're mentally strong, and some luck too. However, smaller teams are more concerned about the sponsors you bring to the team...