The basic, generally accepted guideline says that in Spanish, we use ser with permanent attributes and professions and estar with non-permanent attributes and location. It would be better to say that ser implies identity, while estar implies status, condition, or location.
So here is a more realistic analysis of the general uses of ser and estar:
For personal characteristics (physical or non-physical) and defining characteristics of things or people, we generally use ser:
El perro es grande. Tu tío es muy alto. La casa es roja. Mi hija es muy simpática.
For professions, we generally use ser—even if they may not always be permanent, professions are considered to be part of people’s identity.
Pedro es dependiente. Mi hermano es estudiante en NYU. Yo no soy cocinero, soy cantante.
For people’s feelings, or for condition/status of things or people, we generally use estar:
Mi padre está muy cansado. Ella está triste. Estoy preocupado.
For location, we always use estar (even if it’s a permanent location):
Yo estoy en Nueva York. Mi tío siempre está en su casa. La Casa Blanca está en Washington DC.
With some specific attributes, we can choose to use either ser or estar, depending on what we mean:
María está feliz means she is happy now; it is her “current condition.”
María es feliz means being happy is part of her identity; we are making it a defining trait.
This is commonly done with feliz, guapo, hermoso, gordo, delgado, fuerte, débil, viejo, alegre, and nervioso. A special case would be aburrido: estar aburrido means being bored, while ser aburrido means being boring.
Unfortunately, there is no specific or logical rule that tells us which adjectives can work with both ser and estar.
