Well you could read forge's official docs. They are not exactly a tutorial though.  Apart from that not really, I haven't seen any good tutorial. Even praised modders like McJty make numerous mistakes in their tutorials and enforce cargo-cult programming. I guess the best way to learn is to consult forge docs, look at some open-source mods that are trustworthy, look at vanilla and ask on these forums. I could recommend some repositories I've looked at and they look fine to me - here, here,