One common problem involves adding or extending behavior aftersometimes long afteryou've implemented a class. A similar problem requires you to tack on behavior dependent on the features of a class but that doesn't belong to that class. Both problems have the Visitor pattern written all over themand if you implement it, you'll find that the Visitor pattern provides excellent results.
The Command Behavior pattern lets you encapsulate behaviors within a presentation layer, making it much easier to organize, track, undo, and invoke those behaviors however you like. It's a freeze-frame remote control for your GUIs.
VB6 can be prone to disorganization and the State behavior pattern is a consummate organizer. Use it proactively to prevent spaghetti code or reactively to manage code complexity.