Not a Mini-specific question, but a good question anyway so let me give this a shot. The challenge isn't necessarily finding the files, but knowing which files are safe to remove. If you are not sure, I'd recommend leaving them alone. It's always best to move files instead of delete, until you know for sure they can be removed. Always have a backup at the ready (good advice no matter what).
If you're lucky, the developer might have hidden a uninstaller app inside the .pkg or possibly in the .app file. Right-click the .pkg, select "Show Package Contents" and look in the folders for an uninstall app or script. Do the same for the application itself and see if something helpful is in there.
But even if you do find an uninstaller, sometimes they don't get rid of everything so there's other things that can be checked. I recommend a free, very nice utility called Suspicious Package that allows you to look inside .pkg files and see what they are installing: http://www.mothersruin.com/software/SuspiciousPackage/get.html
Look at the Use and the FAQ links for more information. I am not affiliated with the developers, I just feel this software is worth checking out.