Simon is a hands-on software architect and a senior consultant at 
The Elements of UML Style
Scott Ambler (author of The Elements of Java Style) has written a book called The Elements of UML Style that covers guidelines for developing the various UML diagrams. Not come across this one before but for 8 pounds I might to have to order a copy.
Re: The Elements of UML Style
Excellent book. From the preface, section title Purpose: "This book describes a collection of standards, conventions, and guidelines for creating effective UML diagrams." It meets that goal very well.
Scott co-wrote The Elements of Java Style, as well, and it's another good one to have, and is the same size/price. It's better for beginner/intermediate Java programmers, but but even advanced users might find some useful tidbits.
Re: The Elements of UML Style
Mats - I did mention that they're good only for beginner/intermediate. Pro folk who are jaded like you don't need it. A couple of people I work with that are marginal java coders read the book and improved their code significantly afterward.
Just like VB programmers, you'd be surprised how many people out there are working in Java without a CS/CIS degree or any knowledge of what constitues good programming practices.
