How to build a Debian/Ubuntu package from source?

I have the source of a program (taken from cvs/svn/git/...) and I'd like to build a Debian/Ubuntu package for it. The package is present in the repositories, but: * It is an older version (lacking features I need) * I need slightly different compile options than the default. What is the easiest way of doing it? I am concerned about a couple of things * How can I check if I have listed all the dependencies correctly? (I can get some hints by looking on what the older version depended, but new dependencies may have been added.) * How I can I prevent the update system installing the older version in the repo on an update? * How I can prevent the system installing a newer version (when its out), overwriting my custom package?