Selective breeding is done when you harvest seeds from a pod that you want your future pods to look like, taste like, and exhibit the same heat. You should select the best looking pod (in your opinion) and wait until it is fully ripened, then harvest seeds from that pod. Take plant growth habits into account, however, you need to select a pod based on your desire. If you want tails, then select a pod that has the baddest, gnarliest tail you can find, and pull seeds from that.
A lot of growers here do that. Keep in mind, you may get a cross if you are not isolating, but most of the time that is just an added bonus.