My cookies always go flat and crunchy. How do I get fluffy soft cookies?

Here's a chocolate chip cookie recipe that always comes out chewy.
http://www.marthastewart.com/344840/soft-and-chewy-chocolate-chip-cookies

I posted a recipe here that basically covers what I mentioned: http://food52.com/recipes/18364_sadassas_chocolate_chip_cookies_with_pecans_cinnamon

Any chance your oven could be off? If your oven runs a little hot or if the dough gets too warm the cookies will spread too much and get flat. Crunchy probably means you are using butter and/or maybe shortening? I'd suggest getting a thermometer to hang inside your oven to see if the temperature is accurate. And if you replace a 1/2 cup of the butter with a 1/3 cup vegetable oil your cookies will be softer (I do this all the time). Also really cream the butter and sugars together well with an electric mixer before adding the oil for fluffiness. Increasing the brown sugar to 1 cup and decreasing the white sugar to a 1/2 cup will get them softer too. I hope these tricks are helpful ;)