A great book which explains the principles (and some details) of using OpenGL upon embedded devices.
The book is nicely paced and covers some basic graphics concepts before moving onto details of vertex space, drawing buffers, textures and more. Each chapter contains background context, moves into OpenGL implementation, and covers API reference in good detail.
There is some iOS-specific code, but it not a distraction. I have used the book to create 3D for an Android software, and it was extremely valuable.