First of all Drain water from urad dhal+fenugreek seeds and add it to the grinder. When adding make sure grinder doesn't get stuck. Then Sprinkle water then and there and grind it for 40mins in total. Keep sprinkling water while preparing in between at regular intervals. The batter should be light and nice.
Collect all urad dhal batter in a container. Then Now drain water from rice and add it to the grinder, sprinkle some water and start grinding. Then Grind it for 30 minutes and keep adding water in between grinding and also grind it smoothly with a slight coarse texture. The rice batter should be slightly thicker than urad dhal batter.
Now take the rice batter, urad dhal batter and add salt and mix well. Then keep it in a warm place to ferment well for atleast 10 - 12 hours. If you see the batter would have raised well and now your idli dosa batter is ready to use.
Take a ladle full and add it to the idly pan and steam it for 10-12mins. Sprinkle little water around it and carefully slide around the idlis around the edges