When should I use ser and estar in Spanish?

Ser is used for concrete facts and descriptions of things that are not likely to change.
E.g. He is tall - Es alto. This uses ser as being tall is not something that changes and is usually a concrete fact about a person
He is from London - Es de Londres. The nationality or birthplace of someone is considered to be a fact that does not change, therefore ser is the correct verb in this example
Estar is used for moods, locations and things that can and are likely to change
E.g. She is tired - Está cansada . Estar is used here as the person is only tired at the time the person is saying, this is her mood and is something that is likely to change
My phone is in my bedroom - Mi móvil está en mi cuarto. This is giving the location of something, so we have to use estar