usually all software for 3D has a polygon reducing option which makes a ship real lame if you use that tool. duno what you are using so I cant help much.
but since you are a beginner, consider about following often comited mistakes;
-useless poly: useless poly hidden within or behind another face, delete them
-double sided face; if for some reason, you have double sided face, delete them
-copy-paste multiple hidden face mistake: if you somehow copy pasted a same object multiple time and forgot to delete a certain face that accumulated invisibly at a same position, delete them too!