Ser vs. estar is hard for all new Spanish learners, and one effective way for them to learn is to use the acronyms DOCTOR and PLACE and then practice using them in context.
This activity includes an explanation of DOCTOR and PLACE memory devices with examples and the rhyme, "How you feel and where you are, always use the verb estar."
It has a page of directions with explanation of three different ways that the cards can be used. Students can quiz each other in pairs or make a game out of it by having one student show the card and two students compete to see who can answer it more quickly. With my students, I started with the first example on the directions page (choose "ser" or "estar" and then say the justification), and then had students who were doing that easily start playing using the second or third examples of how to use the cards (explained on page 2 of the download). You can probably come up with different ways to use them as well.
Each card has a short sentence that's missing a conjugation of either "ser" or "estar" (La casa __ grande.) on one side. On the other side, each card has "ser" or "estar," the justification from DOCTOR or PLACE, the keyword translated to English, and the correct conjugation of the verb (ser: characteristic (big) es). All of the vocab should be familiar to second semester Spanish 1 students (or Spanish B for middle school). The purpose is to practice the verbs, so I kept it simple.
The card pages need to be printed back-to-back or glued back-to-back. The right and left margins are off by a tiny fraction of an inch, but they should line up very close. Have the kids cut carefully when they cut them out. Notice that they're not in order on the pages, and this is on purpose so that when they go back-to-back, they line up correctly. I've printed them out and used them with my students, so I know that it works. Card stock will be better than regular paper so that students can't see through.
When I used this with my students, we had previously taken notes on DOCTOR and PLACE, and I gave everyone the first page as a refresher. I had printed out pages 3-6 back-to-back so that there would be enough for kids to work in pairs. I had students cut out the cards and put them in plastic ziplock bags when we were done. If they're on card stock and the kids take care of them, you can reuse them.
Make something fun out of a tough-to-remember Spanish skill!