If you’re new to Groovy, check out our Groovy Basics Docs. It’s not complete Groovy documentation of course, but does contain a lot of tips, tricks, and information about working with Groovy.
Also, check out @pstuart’s Live Code Fridays edition on Groovy: Live Code Fridays 11/6/2015 8pm EST
All of the Live Code Fridays are good and worth checking out.