I'm working in some Debian packages and at some point I'd like to add optional dependencies, e.g. if foo-pkg is marked as to be installed at the same time as my-pkg let foo-pkg install first and then continue with my-pkg, if foo-pkg is not available or not marked to be installed just continue.
I could use the Recommend: field but as far as my tests has gone it doesn't force apt-get to install foo-pkg first, also, I don't have control over foo-pkg, any ideas?
Why do you want your package to be installed after? Does your postinst configure your package differently if it finds the other package is installed? If so then you can use a trigger to cause your package to be reconfigured any time the other package is installed.
Follows some documentation: