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Just read one of your replies "that's the way the cookie crumbles" how life treats you sometimes. :)

Seriously though. It could be your first step creaming the sugar and fats together until light and fluffy.

This is very important so the flour and other dry ingredients mix well. Also chill the cookie dough overnight if possible before baking and see if that helps. Flours are different not all the same. Some are softer and others harder. Measure accurately that could also be a problem. The way your oven bakes do you have a way to test and see if it's accurate. When you set it for 350 does it register exactly or is it off. Get a thermometer to be sure it's right. Under baking and over baking could be it. Bake cookies in the middle of the oven not too high or too low to prevent over browning the bottoms or under browning the tops. Good luck..get back to baking. Have a great summer!

Just thought of another important idea. Some people use margarine spread for baking and it's not a good choice since it has lots of water in it. Not enough fats. So use unsalted butter or shortening like Crisco whatever your recipe calls for but not margarine spread!

Nope. That's just the way the cookie crumbles.

Depending on your altitude and what kind you are making they will do that but a good way to avoid that would be to add a tbs of oil or water