I use three rules when harvesting does, after having done a good bit of reading on the subject along with many years of observations. First, I only harvest does at the tail end of our seasons, hoping not to blow stand locations by shooting early on and also allowing the maximum amount of does to still be around for the rut, hoping to attract more bucks. Second, I no longer shoot lone does because it is too easy to shoot what looks to be a good sized doe and have it turn out to be a big button buck, thus completely defeating the purpose of shooting a doe to begin with.
I now only shoot one from a group of does instead. Third, I take the biggest doe in any group, figuring it to be the most mature & healthiest and also being the one most likely to drop twins or triplets 6 months hence. If you shoot a small doe, you are likely only trimming the herd by one. If you shoot a large mature doe, you are likely trimming the herd by 3 or 4.
My rules, but of course YMMV.