First recommendations for Blender and Avastar Newbies
Also explore the documents mentioned below while you slowly step deeper into the topic.
Getting started with 3D
New to Blender?
First steps in Blender
This informative video is about some of the most common pitfalls and how to get out of them once you apparently stepped out of your workspace.
CG cookies tutorials
cgcookies has free tutorials but also provides a paid subscription. Good for the enthusiasts who really want to learn Blender from the ground up.
Agenzasbrothers Tutorials auf Deutsch
Comprehensive set of tutorials for blender in german language:
New to Modelling?
Create a Mesh Clone
This tool is included in Avastar. You can create a fully functional SL Avatar clone with 2 mouse clicks.
Note, the character is CC-BY3 (owner is Linden Lab) which means it can be reused for free, but you can not put any sort of private license on it. You are allowed to modify, upload to SL and resell this character in SL.
Use the MakeHuman Tool
A tool for creating human characters. Open Source, characters can be reused in any other virtual world for any purpose (including commercial reselling)
Model your own Mesh Head
A Youtube tutorial about modelling. Recommended by other Avastar users
New to Avastar? The Essential Tutorials
Read at least once:
Weighting and such
Weighting tutorial from Timmi Allen (german)
Weight Painting for beginners