One common question is: "I changed the configuration file, but the new configuration is not being seen!" The solution depends on your configured ServerType. Almost certainly it will be standalone, as inetd-mode servers pick up configuration changes almost instantly (the server is started from the ground up for each connection). For configuration changes to be seen by a standalone server, you need to either stop, then start the server (the hard way), or to send the HUP signal the the daemon process.
Another common question involves use of ProFTPD's <Limit> directive to restrict certain FTP commands. These limits always function in addition to the normal filesystem permissions, not instead of them. If having problems writing, deleting, or updating files, check your directory and file permissions first.