Everyone working with Java should take the time to read the Java coding conventions published by Sun: http://java.sun.com/docs/codeconv/ht...nvTOC.doc.html
Coding to the common conventions will ensure a consistency that greatly aids both the coder and others reading that code.

Anyone designing programs that involve more than one or two classes could benefit from familiarizing themselves with design patterns. An excellent introduction to this is Head First Design Patterns. Design patterns may or may not be appropriate for a given application, but learning about them and their usage will teach you to look at your program organization in a more critical manner from perspectives that you may not have considered at the outset.