Here are some resources and links you may find useful.

Let's Mod Reboot

Pahimar's excellent screencast series that introduces many core concepts of Forge-based modding against 1.7.x..

MinecraftForge Files

You can't mod without these. And don't forget there are handy JavaDoc bundles, too.

ForgeGradle Wiki

There isn't a lot of content, but there are sometimes a few key items and insights that may help you learn something new about the built in features of the build system. And don't forget to read the code itself.