You mentioned Bayern and NM, both ships that I played through (altho Bayern much more recently than NM). The Bayern is basically a floating tank. You are very free to challenge other T7 or less BBs by just walking up to them because their guns won't be able to do much to you if you angle. However if you get within a reasonable range (10km or less) it's quite easy to get citadels on them aiming at their waterline, especially with your higher ROF. Bayern also just smashes cruisers.
One of the important things you learn in a BB is being patient. You don't get the constant stream of shells like you do in other ship lines. You need to maximize the value of each salvo. The most important piece of advice I can give is learning to anticipate your opponent's turns. If you properly anticipate a turn you can easily blap a cruiser or BB and get those high damage numbers you keep seeing. Think about how you would move if you were them. Which way they have to turn because of torpedoes, islands, etc. Take advantage of that.