I get asked a lot about developing plugins for Minecraft servers, so i am writing a large in depth tutorial on the subject in a public Git repository for anyone to read. Please be aware that this will continuously be in development so it will have frequent changes and at this point it is still in the very early stages so a lot is missing.
Main Page: https://lab.lawlsec.com/Docs/Spigot-Development
Categories
Code: https://lab.lawlsec.com/Docs/Spigot-Development/tree/master/Code
Project: https://lab.lawlsec.com/Docs/Spigot-Development/tree/master/Project
The Project category is probably the best place to start as it contains a "Quick Start" list right on its main page.