I live at a high elevation (right around 5,000 feet above sea level) and I've found the following high elevation tips very helpful in my baking. I wrote these tips on a 3 x 5 card that I pull out with whatever recipe I'm using. Now, my cookies are no longer flat : )

Increase the baking temperature

Decrease the amount of baking soda or baking powder

Decrease the amount of fat and/or sugar

Increase the amount of liquid and/or flour

Lately, I've been baking a few loaves of bread at home every 2 weeks or so to help save on the cost of groceries. I use a few loaves right away and then freeze the rest to use later.

Since I started adjusting my bread recipes for elevation, the bread has always turned out really well.

Using bread flour (hard/ high protein/ high gluten flour) in cookie and cake recipes also helps.