Learning at least the basics of Java first is definitely necessary, although it will be easier if you have other programming knowledge. After that, just a few things I've picked up recently:
Tutorials: Looking at some tutorials/example mods will get you the basics of modding. A few good resources that I've found:
I've also found it to be very beneficial to join modding Discord servers. You can ask questions and get help from some of the best modders out there. A few good servers would be the official Forge server or the MMD server.
Above all, the Forge docs should be your #1 source, since they are official. After that, just be smart about what you do, and don't get mad if people seem rude when helping you. Chances are, they're not trying to be.