For just starting, those are pretty good. Better than my first ones. Ooh, look! A sphere! Anyway, what program are you using? Just wondering. So, where you go from here really depends on what you intend to use it for. If it's for a ship sprite in EVN, then you probably want to add a little more detail, but you don't need that much, as it's going to be zoomed out quite a bit. If it's for a still frame, like a landing pic or the shipyard pic, then you need to add quite a bit more detail. Some suggestions.
Missile tubes! Everyone likes missiles, and their variants. Torpedoes, rockets, etc.
Even better, external missile racks. Looks really awesome.
Armor plate it. Add some obvious plates. It's not important to be aerodynamic in space.
My specialty, form-fitting add-ons. Find a nice, straight section of the hull, then make 90 degree turns to all of the surfaces. Make a set of faces parallel to it, but a bit bigger. Now extrude it, and use it as a mounting for all sorts of stuff. I generally do lasers and missiles.
Sensor rods. Very delicate tubes, sticking out towards the front of the ship, starting about halfway back.
Hatches. Hey, you want to be able to get on, right?
Fins. Yeah, there's no need, since you don't need to be aerodynamic, but seriously, they look cool. The three classes of ships, fighter, cruiser, and battleship, take differant stands on this, though. Fighters are very sleek, and generally have some very cool fins sticking out. Cruisers generally have no fins, but are very flowing, smooth designs. Battleships, of course, don't care about any of it. When you weigh in at 500 tons, you don't bother making it aerodynamic. It doesn't help.