So far, I've encouraged would-be-evangelo-advocates to enjoy Ubuntu themselves every day, to skip Colonel and Yak-like historical comparisons, to pronounce Ubuntu in a manner respectful its origin (oo-boon-too), to be selective when choosing an advocat-ee, and to direct people towards their local community. The tip-fest continues with...
Do not compare.
Never compare Ubuntu with other operating systems, free or not. When you do, you draw people's attention away from your message and towards a competitor's (even if a friendly one). You also frame Ubuntu in their context, which is usually "just software".
Don't name competitors' names. Refer to their products only if asked specifically, and only in the general sense. And if this happens, keep steering your conversation back to Ubuntu.
If you do this, you'll be able to spend more time spreading enthusiasm about Ubuntu rather than re-hashing nightmarish experiences with other systems...
Could there possibly be more?! Check back for Tip #7 tomorrow. It will be something I've learned the hard way by trying, failing, re-thinking, and then trying again.
Be an Advocate extraordinaire! The Ubuntu Advocacy Kit awaits:
"Ubuntu Advocate" image CC BY-NC-SA 2.0 by "garak". http://www.flickr.com/photos/garak/6560558859/sizes/z/in/photostream/