Ser & Estar are surely among the most complex concepts to grasp in Spanish and at the same time are fundamental to it so we see ourselves exposing our students to these complex concepts since the beginning of our classes.
We can start by talking about this complexity (without passing on any fear to our students), and giving your students a couple of rules to follow:
Ser: is used for facts and characteristics
Estar: is used for perceptions and opinions
In this case we have to recommend to stay away from simplistic acronyms that won't do the job. It is better to approach this learning conceptually.
“There are no magic tricks available to teach the difference between ser and estar, and it gets more complicated to explain these concepts to an English native speaker as English has just one verb "to be" for the same use.”
There are so many resources out there to learn/teach "ser & estar", here we have tried to compile what we think it works best at early stages.