Bummer ... Cookies

So, I'm in need of some baking advice from anyone out there who knows the ins and outs of baking cookies better than I do.

In the past, I've baked these Ginger Cookies that have turned out really good and fluffy. This year, I have tried making them again and both times I have tried making them, they have turned out really flat. They still taste really good but they are totally flat. And I just don't know too much about baking to adjust the recipe accordingly. Any suggestions?