I just realized that I don't know if I should add more or less water next time. What sort of signs would indicate that I should add less water and what signs would indicate that I am using too little water right now?
Rice cookers usually use the "absorption method", in which by the end of the cooking, all of the water has been absorbed into the rice.
If, by the time the rice is the texture you want, there is still liquid in the pan, then you used too much water. But it's OK; just pour the excess away and leave it a couple of minutes for the rest to absorb/evaporate.
If there is no liquid left, but the rice is not as soft as you would like, then you did not add enough water. Sprinkle with boiling water and allow to cook for longer.
With the absorption method, rice is pretty foolproof: twice as much water as rice -- by volume, and one teaspoon of salt per cup of rice. The packet will tell you how long your rice should take.
Things that can go wrong when using the absorption method in an ordinary pan:
For basmati rice, I use my g/fs tried and tested handed from generation to generation method of: