I want to move my server to another machine, which files should I copy?

The following files and folders need to copied if you want to retain the respective information:

licensekey.dat
This file contains your license. You may not have this file, in which case you don't have to copy it

query_ip_whitelist.txt
Whitelisted IPs for the query interface

query_ip_blacklist.txt
Blacklisted IPs for the query interface

files/*
Any Icons, Avatars and files that were uploaded to the server. Be sure to copy the entire folder including any subfolders and files inside.

ts3server.sqlitedb
The database. This file is the most important one and contains all the information about virtual servers, users, permissions, channels and groups etc. All Settings of the server instance and its virtual servers are contained in this file.

*.ini
Possibly existing file(s) containing startup parameters and database configuration. These do not exist by default

tsdns/tsdns_settings.ini
The configuration for the TSDNS service. This is only needed if you actually use TSDNS.