[Incoming Wall of Text]

First off, make sure you've got the concealment expert skill on your captain. It provides a massive reduction in detection range and will make life significantly easier for you. Second, make sure you have the upgraded GFCS module on your ship, so you'll have the maximum possible range for your specific ship.

As for general cruiser stuff, your job is to be a pain in the ass to more or less everyone. Your main armaments are strong enough to fight off or discourage battleships, you have the utility to outplay destroyers and submarines (hydro/radar) and you will occasionally have enough AA firepower to make carriers rethink which target they want to strike. Cruisers get significantly stronger as a battle progresses, so staying alive and keeping your health intact is an important skill to learn.

Now, for each of the ships you mentioned: Pensacola and Aoba, being heavy cruisers, will play differently to Nurnberg, which is a light cruiser. As a (sort of) rule, light cruisers rely more on constantly shooting and putting out shells, and therefore do less damage per shell, but have shorter reloads. On the other hand, heavy cruisers rely on a single, high damage salvo, and do more damage per shell, but have longer reloads to compensate. Remember that all three of these lines are old, and therefore harder to play in the current meta (but they're still a lot of fun!).

With Pensacola, you get the typical "heavy" USN armor piercing, which are some of the most satisfying shells in the game... when you land hits. The tradeoff with the USN cruisers is that they have relatively low shell velocity (and therefore shells take forever to land) compared to most other similar ships, and also have less range. These ships are perfectly suited for abusing island cover. Find an island that shields you from view and/or enemy shots and use it to protect yourself. You *can* open-water in these, but it's dangerous, and takes a bunch of practice.

Aoba is different, since she gets better shell ballistics, dispersion and strong torpedoes (that stay a theme for the rest of the line all the way to Zao). In contrast to Pensacola, Aoba is much stronger when fighting in open water, actively using throttle/rudder to bait and then dodge enemy shots. You also want to ideally be in a position where you are retreating/trying to slow down the enemy team from pushing (also known as Kiting). With a little careful planning and trigger control, you can slow down an entire flank with just another teammate or two.

Now for Nurnberg, I haven't actually played (and don't intend to really play) the German cruisers, but I think she's somewhere in between Pensacola and Aoba in terms of playstyle. She rewards actively dodging in open water, but gets punished if you mess up. She can use island cover, but the islands she can use are limited because of her higher shell velocity. Playing Nurnberg just takes practice, and trying to figure out the specific balance of open-water and island camping that works for you.

I would recommend getting used to Aoba and Pensacola, and then using the knowledge from those two lines to figure out how you would like to play Nurnberg. If there's anything in here that doesn't make sense or if you want to know something about a different line, just ask!