I have been trying to make chapattis (an Indian flat unleavened bread, somewhat like a wheat tortilla), using the following recipe for the dough: 300ml water, 250g whole wheat flour, 250g white wheat flour, pinch of salt. The dough rolls out fine, but the cooked chapattis turn out rather hard and/or rubbery instead of nice and soft. Any ideas why, and what I can do to improve the result? 
Oh well, I make chapatis everyday, even when I bake a Pizza or a cake.     The dough for making chapatis and stuffed and plain parantha and even poori is same. Until and unless you are trying some thing fancy like bhature you just need water and wheat flour.   As I am used to kneading dough w/out any measurement I cant suggest you measurements. I knead the dough till the time its firm enough to stand in a round shape. More over I take a ball of dough and throw it on granite counter with some force it doesn't loose its shape.     Now the temperature of griddle matters a lot. I keep it on a medium heat for chapatis and high for paranthas. Roll out a chapati and place it on preheated griddle. You may need some flour while rolling out the chapati. Leave it on griddle for 10-15 seconds. Turn the side and leave for another 15-20 seconds. Turn side third time and you should see the chapati puffing up with steam. With this dough you can make chapatis, plain paranthas, stuffed paranthas and poori.   On a very special occasion my Mom used to knead the dough with milk and or ghee, a kind of clarified butter. Dough kneaded using milk and ghee is normally used for purees. Apart from all the technicalities you may have practice a while. It took me a month to roll out a perfect round fluffy and soft chapati. Best of luck :)  