Acronyms for Estar / Ser
I found these acronyms helpful when I started learning Spanish. I also find it interesting that Estar and Ser are "introduced" this late in the course. I am guessing they were going with the "you'll see it used enough that you'll get a feel for it" approach? Either way, these should help you understand and remember when they use Ser/Estar until it becomes natural.
General Ser Rule
Ser is used to classify and identify permanent or lasting attributes. If the general rule isn´t specific enough for you, think of the acronym DOCTOR, which stands for Description, Occupation, Characteristic, Time, Origin, and Relationship.
General Estar Rule
Estar is used to indicate temporary states and locations. If the general rule doesn´t suffice, think of the acronym PLACE, which stands for Position, Location, Action, Condition, and Emotion.
More thorough explanation (and source):
This website is good reading for understanding Spanish grammar (also look for para/por uses and acronyms)