Here's the tutorials I mentioned, they are fairly basic but may prove helpful now that you've familiarized yourself with the Blender interface.

http://www.4shared.com/dir/5124164/202e1b1e/Tutorials

The Simple Modeling in Blender - Part 1 & 2 are the most pertinent to what you are attempting.

The  Creating Clothes Sans Poser is applicable but is mostly an exercise showing how to hack a .cr2 file to create rigging for your clothes without using Poser. It works but has limitations.

Retopo in Use explains how to use the retopo feature in Blender to reduce the poly count by creating a lower density mesh that conforms to  your high poly mesh surface. Good if your clothing has progressed nicely surface wise but is too high poly for ease of rendering.

Hope these are of some use to you.