Gaia Clary of Machinimatrix.org is making a new video tutorial on weight painting for Second Life™. A new post is up on her blog asking for input. See: Weighting with Blender.
The actual tutorial part being worked on is here: Course: Weight Painting (Blender&Avastar).
AvaStar is not required. Plain Blender (2.70+) can be used for the tutorial.
One handy thing is the free ‘blend’ file with example clothes. There is also a free OBJ file with the same models. The models are licensed via Creative Commons Attribution 4.0 with accommodation for the current Linden Lab TOS. The models are not yet weighted, that is for a class activity.