Well, there are two types of score: raw (what you see in the game), and then weighted (what you see in the high scoreboards list, and on Steam, etc, as the primary score). Most likely at some point I may switch it to showing the weighted in the game itself, because that's a more interesting metric. The weighted score is based around a ton of complex factors including the raw score, the amount of time you play (winning faster is better), your kill to loss ratio, if you used cheats or handicaps, etc, etc.
The raw score, what you see in game, is much simpler. It's based on two factors only: ships built and ships killed. Different ships are worth different amount of points, so you get more ships for building or killing a starship, for instance. So, general advice for a better score: fight more!