1.Rice and urad dal ratio is dependent on the quality of urad dal. Urad dal that we use in Coimbatore (India) yields more batter and so we use 6:1 rice:urad dal ratio. But in US, I use 4:1 as urad dal doesn't yield more batter here. Laxmi and Costco urad dals yield good quantity and so you shall either go with 4:3/4 or 5:1 - both these ratios work well for me, and I add 5 cups rice, when I want more batter. Else, I go with 4:3/4 regularly.
2.If your idly is not fluffy (but flat), try to reduce fenugreek seeds from 1 tsp to ½ tsp. If your idly is too fluffy (and porous), reduce poha/aval from 1 cup to ½ cup.
3.Using fenugreek seeds and urad dal-soaked water to grind the batter is important for good fermentation.
4.Never store the batter with the ladle in it in the fridge as it will decrease the shelf-life of the batter.
5.Do not use a large container as more empty space will not aid good fermentation. Make sure your container is filled more than half with unfermented batter so that it rises well to fill the gap. If the gap is too much, then rising will be lesser.
6.If you are using cloth to make idly, once done, put those clothes immersed inside the remaining hot water in idly maker and let it soak until you are done with your breakfast/dinner. This soaking will make the cleaning easier.
7.Approximate water measurement for beginners: Soaking water is just 2 inches above each ingredient. Use ¼ cup water to soak fenugreek seeds and use it fully to grind it. If using ¾ cup urad dal, use 1+1/4 cup water to grind urad. If using 1 cup urad dal, use 1+1/2 cup water to grind urad. If using 4 cups rice, use 1+1/2 cup water to grind rice. If using 5 cups rice, use 2 cups water to grind rice. Finally, to rinse the grinder to collect all the stuck batter, use ½ cup water, add it to batter and mix well. Water measure might slightly vary (plus or minus), as per the quality of ingredients used.
8.Watch the video (at the end of this post) to see an important tip in making perfect idlis in both racks.