Assuming you have Eclipse IDE for Java Developers installed, start Eclipse, click "Help" -> "Install New Software..."
Select "--All Available Sites--" at "Work with:", and navigate to "Eclipse Plugin Development Tools". Select "Eclipse Plug-in Development Environment" by ticking the checkbox in front of it.
Click "Next" to let Eclipse check for any dependencies needed. Click "Next" again to start the installation.
Once that has finished, restart Eclipse.