Living in Denver, how do I adjust for the altitude with my baking?

This guys a life saver! I used to live at 7000 ft so he saved me , and also my poor friends who were subject to my baking:

http://www.kingarthurflour.com/recipe/high-altitude-baking.html

I wrote the high altitude baking section for The Bakers Dozen Cookbook, having lived (and baked) at many different elevations. For your altitude, decrease the leavening by 44%, increase the flour by 6.75%, and increase the egg by 11% (just go ahead and add an extra egg). There was a similar thread a couple of months ago: http://food52.com/hotline/21417-a-question-about-a-recipe-chocolate-bundt-cake

I'm a Denver native so I know what you're talking about. Usually the first time, I will bake a recipe without making any adjustments. If the result isn't great, I will adjust by increasing the flour by 1-2 tbsp and decreasing baking powder/soda by 1/4 tsp. If you increase the flour, you may need to increase the liquid. Butter and oil are usually not changed. I agree with SFmiller - the King Arthur guide is great.

There are several general rules, one of which is that it takes less chemical leavening (e.g. baking powder, or baking soda plus acid) to get the same effect at altitude than it does at or near sea level. Your muffins fail because they're over-leavened: the air bubbles are too big and numerous, the baked batter can't support the structure, and the muffins collapse.

The King Arthur baking website has a handy brief guide to high-altitude baking:

http://www.kingarthurflour.com/recipe/high-altitude-baking.html