The Makefile should do things simply and reasonably. If you can make it a couple of lines shorter or more readable, then do so. Examples include using a make .if construct instead of a shell if construct, not redefining do-extract if you can redefine EXTRACT* instead, and using GNU_CONFIGURE instead of CONFIGURE_ARGS += --prefix=${PREFIX}.

If you find yourself having to write a lot of new code to try to do something, please go back and review bsd.port.mk to see if it contains an existing implementation of what you are trying to do. While hard to read, there are a great many seemingly-hard problems for which bsd.port.mk already provides a shorthand solution.