Sources to improve

http://yugioh.tcgplayer.com/db/article.asp?ID=3438 Article by Joe Frankino about how to approach Judge Calls in the right way
http://www.succeedsocially.com/allarticles#socialskills How to improve Social Skills
http://www.pojo.biz/board/forumdisplay.php?f=14 Q&A Forum
http://www.yomifrog.de/xgm/en/Extended_Game_Mechanics_-_Chapter_1.php A bit old (skip the priority chapter)
http://www.yugioh-card.com/de/gameplay/rulings/New_Terminology_and_card_text_for_webpage.pdf
Konami Guidelines
http://www.wizards.com/magic/tcg/events.aspx?x=judge/archives Articles from Magic Judges about how to improve. Ignore the TCG-Related stuff. ;)