How to customise package source

[Andrew Luke Nesbit <alnesbit@optushome.com.au>]

I want to apply a few of my own patches to the source code of a program
before doing the

$ debian/rules build
$ debian/rules binary
$ dpkg -i ../foo_version-revision_arch.deb

thing.  Is there any resource which describes how to do this sort of
thing properly?

Thanks.

Andrew.