Well yes we all know many ways to hopefully continue to drive your credit score up and be approved for anything you might want or need at a moments notice but really unless about to buy a car or a house I would not worry about the 0% and or your util. if you are using it each month or let something sit because it's 0%  Guess what you got approved for the Discover it card with $3k limit before you started worrying about half of these things above and the fact is including me and possibly some others on the board, You got approved and I didn't so don't all of a sudden get caught up in the constant worry of balance, when statement closes, and not paying before or paying after statement to mess up util. and carry or not carry just for use of the 0% or to make Discover want to give you more credit.... 

Take your $3k, Do as you have done since you turned 18 when it comes to your credit and worry a little more about the nitty gritty of util. and stuff later when you get ready to really make some life changing dealings.

SUPER CONGRATS!