You can avoid infringing on someone else's brand by doing a comprehensive search before using a new trademark and ensuring that your pattern is not too similar to an existing mark. You should also consult an experienced attorney who can help you choose and register a solid trademark. You can protect your brand by registering it with the USPTO and using it in commerce. If someone does infringe on your brand, you may be able to file a lawsuit against them.
If you are accused of infringing on someone else's brand, you should immediately consult with an experienced attorney. You will need to respond to the accusation, and the attorney can help you craft a strong defense.