What is the best way to french braid your hair, (for pigtails and regular)?

My hair is long enough to do this and i know how to French braid, but should i do it when my hair is wet? Dry? Should i try to make it tight or loose? And for pigtails, where is the best "line" along my head to braid? And how can I make it follow that line? Also, I can't make my hair look neat when I add a section of hair to the braid. Any other tips will be appreciated as well!!