Valve posts tutorials and technical specs for DotA 2
These tutorials are amazing. Even if you’re not looking to model characters, they’e absolutely worth reading. The character art guide breaks down a lot of best practices, from silhouette and character gradient to color palettes, areas of rest, and before-and-after revisions. There’s also a good amount of general modeling advice on wireframes and UVing. The texture guide is more of a step-by-step guide to how they create their color maps, and while the particular pipeline is very DotA-specific, it’s a great resource for practicing hand-painted stylization.
Finally, the two spec links cover polycounts, LODs, texture resolutions and so on for DotA-spec models. They also have quite a few sample models (mostly in the character bio pages in Technical Specs) that you can download and pick apart in your own time.
This is an incredibly useful set of resources for anyone who wants to do characters, stylized models, or just wants a breakdown of some of the principles of 3D and design.
(Lots of thanks to Tyler Fermelis for pointing these out to me.)