Roll them really, REALLY thin! As thin as you can get them without tearing up. I roll them on parchment paper because it makes it really easy to transfer them to the pan.
Your tortilla dough should be soft and stretchy. If it's crumbly after kneading you've added too much flour. If it's sticking to your hands, add bit more flour.
If you do not have a tortilla warmer, create one with using a pot with a tight-fitting lid. Stack the tortillas between layers of barely damp paper towels and then place the lid on the pot. THIS IS A MUST, if you want your tortillas to be soft and pliable for days.
Most recipes suggest not using butter or oil on the pan because this will cause the tortillas to become crispy. This is true! However butter gives such and amazing flavor and placing the hot tortillas between layers of damp paper towels will steam them to perfection, making them soft and pliable DON'T SKIP THIS STEP.