I literally just finished COT not even a week ago. 1 start saving money, there's a good chance you're not going to get paid while you're there (a lot of financial problems).
2 get your CAC ID before you go, you can get it once your orders say your active, get a CAC reader while you're at it
3 start running, be able to do your required run, push up, sit up. We lost a few d/t PT test
4 prepare to get yelled at. They start off nice giving you your packet, then they turn on the drill instructor mode at an instance
5 buy ALL and I mean ALL your uniform items, they will have you buy them, they don't have all the supplies, and you're competing with 200 other people for the same stuff
6 good luck