As promised, here are some things that I've been working on too regarding helpful guides for Shipbucket, which I'm going to do as addendum to what acelancelot wrote (the numbers refer back to ace's points):
1. I'm going to add that it might be good to sketch out a real warship beforehand too. Yes, by hand. It doesn't have to be pretty, the idea is to force you to become aware of the systems present. This is purely optional and really experimental at this time.
4. A part of realism is populating your ship with realistic parts to keep it from looking barren. I've labelled all the parts that I can in the drawing below, using one of my own ship designs for now (yes, I totally drew this myself) and photobucket because I'm lazy:
5/6 This is a basic illustration to what acelancelot means:
7. The size of your powerplant will show up as the size of your funnels. Big engines = big funnels. This remains true whether you have steam or gas turbines; diesels on warships seem to be the one exception but I've seen plenty of big funnels on diesel ships as well (typical freighters and tankers, for example).