Great question! There's a review of the usage of these two verbs in Intermediate, Lesson 2, Grammar Point 1. There's also something in Essential Lesson 4.

I'll let Anna add to (and correct, if necessary!) my answer, but the general rule of thumb is:

Permanent things, attributes that don't change: ser
Manuel es de Bolivia. (Manual is from Bolivia.)
Los estudiantes son intelligentes. (The students are intelligent.)
Mi apartamento es pequeño. (My apartment is small.)
Madrid es la capital de España. (Madrid is the capital of Spain.)

Temporary things (locations, moods, physical conditions, attributes that change): estar
Estoy enfermo. (I’m sick.)
Estamos en Madrid. (We’re in Madrid.)
Estás en la casa. (You’re in the house.)
Los estudiantes no están cansados. (The students aren’t tired.)

Another student asked a similar question in th Spanish Forum and I wrote a quick guide on how to conjugate and when to use SER and ESTAR.

I hope this helps! Let me know if you have any questions.