Coding for portability
Writing code that will compile and then run on different platforms can be surprisingly easy. Writing portable code describes some straight-forward steps to take to make your program easy to port to new platforms.
Document based application design
One of the most common use-patterns of applications on modern platforms is that of document-based applications - applications which can have several active user-controlled contexts.
Some familar examples might be a word processor where the user may have multiple document windows concurrently, or a web browser which allows a user to have a number of different browser windows open at the same time.
Document based applications provides information and tips on how to code this style of application.
Using property lists
A regular issue that programmers face is storing structured configuration information, and reading it back. GNUstep has a standard mechanism that can be used for this task, amongst others: Property Lists.