What I have learned is, I add the same amount of yeast and sugar. I add a tad bit more salt, that helps to slow the yeast. But the biggest changes I have had to make is the addition of more liquid, being at higher altitudes often means being in a drier atmosphere, the lower humidity means your flour has absorbed less moisture from the air, and doughs dry out much quicker. If you are used to making bread by hand, then you already know what a perfect dough should feel like and you will automatically know that you need more liquid. If you are used to making bread in a machine, watch your dough, if your machine is struggling to mix and knead the dough, or if it just doesn’t look right, add more liquid, a tablespoon at a time, reach in and feel the dough as it’s kneading, does it feel soft enough? Does it look right? If not, add more liquid. Don’t be afraid to experiment to find out what changes work best for you, don’t be afraid to mess up, it’s just bread, if it falls, then use it for breadcrumbs, croutons, bread pudding, or worst case scenario, feed it to the birds. :)