The mnemonic devices "doctor" for ser and "place" for estar make it easier for students to remember the situations where you would use each verb. Ser's acronym, DOCTOR, stands for Description, Occupation, Characteristic, Time, and Origin. Estar's acronym, PLACE, stands for Position, Location, Action, Condition, and Emotion.
A 24" x 36" PDF for printing is available here.
I made this poster with Adobe InDesign CC.