A pair of tweezers.
And a lot of patience, to wait for the glue to dry, for the paint to dry, for everything.
And take care to tone down the colours a little bit. When you use for instance the original Navy Blue or Battleship Grey on a scale model you'll find that the colours are unrealistic. Because you whatch your model from say one meter, but you expect your model to be on scale distance (probably a few hundred meter). Over this distance the air filters some of the original colours away. Add a bit of White, Sky Blue or Duck Egg Green to the other colours to make them look more realistic...
And if you "weather" a ship, do it subtle. No heavy streaks of rust unless that is historically correct (which it probably won't be).