Make sure you are using Eclipse 4.3.1 (called "Kepler") or a newer version. You can download the Java developer version from
http://www.eclipse.org/downloads/packages/eclipse-ide-java-developers/keplersr1

Select File | Import | Install | Install Software Items From File and choose a locally downloaded copy of 
https://github.com/cgeo/cgeo/tree/master/main/project/eclipse%20installation/cgeo%20eclipse%20components.p2f.

This way you can easily install all necessary plugins for c:geo development.