In the first part of this grammar topic, I introduced to you what SER and ESTAR in Spanish are and roughly outlined the key features of those verbs. But the deeper you´ll dig the more you´ll have to comprehend to take on this challenge confidently. The hardest obstacle is a bunch of adjectives and participles which go with both SER and ESTAR but change their meaning depending on the verb.
I learned my favourite example at the university, SER borracho and ESTAR borracho. By using SER, we refer to a person who is a drinker for a long time. With ESTAR, we only point out someone who had a smashing party and drank a bit. Or more. But when the party is over, that guy would return to normal life and won´t be judged by society. Basically, all ambiguous words like borracho do the same, describing a constant or a temporary state depending on SER/ESTAR. So the best way to move towards better proficiency is just to memorize them. For this purpose, I created two cheat sheets with the most common pairs and hope you´ll enjoy them!