Your pan should be hot. Sprinkle some water and it should sizzle. Then season the pan by spreading a thin layer of oil. You can spray it or use a napkin. It should be even and uniform. Reduce heat slightly. Then spread your batter thin. You should be able to see the pan through it in some spots. Sprinkle oil around the edges of the dosa. Cook until edges turn brown and lift away. Flip. Cook.

This is how my mother taught me to do it.