Clans have a prefix and the suffix "Clan". The prefix should be capitalized as well as the suffix. To create a Clan name, make sure it follows the number one rule of this book:
IT SHOULD BE REALISTIC/MAKE SENSE and/or RELEVANT TO THE PLOT!

Realistic Clan names have the same prefixes as some cat names. But some of those prefixes do not work for Clan names.

Clan Names You Should Not Use

-DragonClan, UnicornClan, GiantClan, ElfClan, GoblinClan

-DeathClan, LifeClan, KillerClan

-LoneClan, FullClan, AloneClan

-HeartClan, LuckClan, CharmClan

-BrightClan (it sounds weird), LightClan, BraveClan

-DemonClan, DevilClan, BadClan

-CatClan, DogClan, WolfClan, HorseClan, SheepClan, DeerClan, BadgerClan, MouseClan, RatClan

-MilkClan, HoneyClan, WaterClan (it sounds ridiculous), OceanClan, SeaClan

-ClawClan, FangClan, PawClan

These Clan names are unrealistic. The Clans that include "Heart" or "Brave" are just plain stereotypical. They are directly showing that the Clan named "BraveClan" is the best Clan there is. "DarkClan" may be used because it's close to "ShadowClan".

The following Clan names are good for writing a Warriors fanfiction:

-BrambleClan

-StreamClan

-GrassClan

-PineClan

-PoppyClan

-SandClan

-MistClan

-GorseClan

-OakClan

-WillowClan