How to name an AD domain

The rules are mainly given from DNS : acceptable naming conventions for domain names include the use of alphanumeric characters (the letters A through Z and numerals 0 through 9) and the hyphen (-). A period (.) in a domain name is always used to separate the discrete parts of a domain name commonly known as labels. Each domain label can be no longer than 63 bytes. The first label may not be a number.
Extra restrictions must be considered :
_ If you want that the NetBIOS domain name corresponding to your domain reman simple, use less than 15 characters. _ don't use the same domain that you use on the internet, but in order to avoid that it happens after, book the domain you use internaly on the internet _ don't use the prefixe .local