What are you trying to do? We can probably offer advice. For the most part, at least to start out in your initial ship (likely whatever you upgrade to after your Sidewinder), you should build for a purpose and make money off of that. You have options like exploration, combat (bounty hunting, Combat Zone farming, etc.), trade, piracy, smuggling, ferrying passengers (kind of goes along with exploration).
Bottom line, you'll notice there's four categories you have ranks in: Combat, Trade, Exploration, and Arena. Arena is just the extra arena mode, so as far as the main game goes, don't worry about that. The others are the three general categories of what you can do, and having higher ranks in each gets you various stuff.
I personally am Deadly 22% in Combat. Deadly comes right before Elite, so hopefully I can reach Elite soon.