If you already know C/C++, checking out all the tutorials at doc.trolltech.com is pretty essential. You should be familiar w/ C++ syntax, so you'd just need to familiarize yourself with how Qt works, how qmake compiles, SIGNALS & SLOTS (the essence of Qt), and most importantly, Qt's native classes.
That being said, I've found most Qt books to be pretty crappy (note that I've not tried any since Qt 3.2 or so though, so they may be better now). My C++ knowledge was also basic at best back then.
The Qt-interest mailing list (you can subscribe from Trolltech's page) I've found to be the best source for Qt relate stumps.