You need to develop an eye for accuracy... For example the star on one side of your fuselage was way too high, and the other side maybe too low.
One example is that you've added some details like panel lines and what looks like some paint chipping near the rivet lines, but on the other hand you've got no stains, leaks, from exhausts, oil, hydraulics, gun barrels, and so forth.
For the first issue, look at some reference photos. I wouldn't simply say "I made the stars bigger!" unless you looked at a reference or photo, and realized they were too small before. I would also suggest looking at the stars you have on your wings. They're not true stars (the angles are off, some thinner, some thicker, off-angle). If you're having troubles put a template layer underneath of some picture or something, and trace a new layer on top of that (to get the right size/angle/proportions).
For the second issue you'll need to experiment and see what you can pull off. Forum feedback will be VERY useful for your first few skins, and in fact most experienced skinners still look for forum feedback.