This something that I've needed a little refresher on. Both modifying existing meshes and creating new ones. My friend and fellow modder, Vince Bly, created some lessons that are easy to follow and very informative. They were originally created for Oblivion, but I have used the knowledge gained for Skyrim as well.
This first one, taught me a lot about how to use NifSkope.
The House Modder's Tool Kit by Vince Bly - The House Modder's Tool Kit (HMTK) provides a way to create new content for Oblivion without having to master a 3D modeling program like Blender.I wrote a follow up, mainly to help with the math part of HMTK.
House Modder's Tool Kit Explained by Phaedra - This tutorial is a further explaination of how to use HTMK by Vince Bly.
With this one, I learned how to create new models, including how to texture, add collision, and import them into a game.
Wings3D for Oblivion by Vince Bly - Wings3D for Oblivion (W3D4O) is a tutorial that provides the 3D modeling and NifScope procedures needed to create new 3D content for Oblivion.
Scripting in Skyrim is done using a language called Papyrus. I've done a small amount of scripting in Morrowind and Oblivion, mostly modifying existing scripts to fit my needs. But now I want to create my own scripts for Skyrim. Here are a bunch tutorials that I've found and will be studying.
TES Alliance's Papyrus 101 forum - There are 3 Classes stickied at the top of the forum, the first teaches the basics of scripting. You can also post questions if you need help.
Cipscis' Skyrim Tutorials - There are 4 Papyrus tutorials on his website.
Creation Kit Wiki, Category: Papyrus - A lot of information on Papyrus created and maintained by the modding community.