The fastest thing to do is ask in the forums.
I'll second this. Got Sunburn with very little experience in 3D - just what I'd read in several books/tutorials but never tried writing myself, but from the examples and the forums I'm getting the hang of it. Got a nicely lit spaceship flying around the dojo with player input, newtonian physics (imagine Asteroids in 3D!) and all within a few hours! I can relight the scene within minutes, I can add scenery, and all without touching the code. For me to be able to do that is a true testament to the power of Sunburn!
Seems the best way to learn really is to open up an example project, such as the Dojo and simply play around with it. Model a box, get it displaying via code or add objects via the editor, then the same with lights, then get a model moving, then make it respond to player input and so on..
Between the example projects, sunburn forum (note - you really do get replies very, very quickly!), the XNA forum here and google, you can get a simple 3D scene up and running in no-time. More advanced questions, or even beginner questions, the sunburn forum is the best place. It seems like most questions get at least a reply within a few hours of being posted.
Though I do believe that some tutorials would greatly benefit those starting out. The first few days I felt out of my league doing anything other than moving lights about in the editor..