I would die to go to Katsucon, but alas. I've gone to a lot of cons, and my main word of advice is don't be afraid to ask people how their con is going or to compliment their cosplay. Worst case is they're busy and move along quickly, unless they're just total chuds; and that's on them. Also, make sure you're not forcing your way into conversations; I know that's a lot of congoer's pet peeves. Lastly, don't be afraid to ask to take photos with cosplayers! Most of them expect it so the very worst case is them being like "nah not right now". Also have so much fun and create insanely cool memories B)