Before starting to pour dosa rub with a half sliced onion all over the pan so that it becomes a nice coating that your dosa will come clean without sticking.
The consistency of the batter should not be thin like aapam batter,it should be thicker than that.
You should be able to spread easily.
In hotels they add some sugar for taste and color but no need to add it comes out crisp without it for sure.
Before pouring the batter rub the pan with oil smearing cloth and then spread the batter.
If the pan is heated up too much and if you are poring the batter by this time then the batter will clump up!so use a flat bottomed ladle and the pan should be under medium high heat when you are making dosa.