The Arabic Treebank team at the Linguistic Data Consortium has significantly revised and enhanced its annotation guidelines and procedure over the past year. Improvements were made to both the morphological and syntactic annotation guidelines, and annotators were trained in the new guidelines, focusing on areas of low inter-annotator agreement. The revised guidelines are now being applied in annotation production, and the combination of the revised guidelines and a period of intensive annotator training has raised inter-annotator agreement f-measure scores already and has also improved parsing results.