Take your time. The best tortillas aren’t quick, 15 minute affairs. But they’re worth the extra effort.
Lower the heat. The first time I cooked tortilla I had the heat too high, similar to when making other egg dishes. This resulted in a rubbery tortilla.
Cook the potatoes and onions separately. Many recipes cook them together, but to get each to its prime Spanish omelette point, I think it’s worth washing one more pan.
Use room temperature eggs. In Europe, many people don’t refrigerate their eggs at all. Recipes are meant to use room temperature eggs and it does make a big difference.
Let the egg, potato, and onion mixture sit for at least 15 minutes — minimum! This makes a HUGE difference to the final result. It is a must.
Don’t fear the flip! You have to go forcefully and quickly to make it happen. Don’t be afraid!
Use a small frying pan and make two tortillas when starting out. I love this tip because it makes the flip so much easier (the pan is lighter, any dinner plate will work, and if you mess up the first time you still have half the batter left!).
Use great quality olive oil. Considering the potatoes are slowly cooked in olive oil, they absorb a lot of it. If you use good quality olive oil everything will be tastier and much healthier too.