The first step is to know the game. You have to know every unit and what it does, what it's good against and what it's not good against. Even if you don't play a specific faction, you have to know what its units do otherwise it's very difficult for you to counteract the opponent's strengths.
To some extent, every faction has similar units. Everyone has a carrier cruiser, a light frigate, a long range frigate, and so on and so forth. For the most part, the differences between them are more subtle. Where you need to be cautious, though, is with support cruisers and capital ships that have unique special abilities.
You also need to know how to build a strong economy. Most players tend to over-emphasize technology and trade ports when they're first learning the game. There is nothing wrong with tech or trade, but the real secret to a powerful economy is much simpler: colonize colonize colonize. At the start of the game, you should be scouting voraciously to discover the layout of the solar system. You need to find out where the resources and strategic locations are, and formulating a plan. I've played many matches where victory and defeat came down to how each player planned his expansion in the first 10 minutes of the game.
The first thing you need to do at the start of the game is pick a capital ship. It is generally regarded that you have two choices: carrier capital ship, or colony capital ship. The colony-class capital is more of an economic choice, speeding up your colonization and ultimately giving you a more powerful economy. The carrier class is the ideal capital ship for early-game combat. If you think you'll rush or be rushed, you should pick a carrier-class. Beginners often make the mistake of choosing battleships as their first capital ships. The battleships aren't bad later in the game, but they're heavily outclassed by carriers in early combat and don't give you the speedy colonization bonus.
Once you get moving, you can start adding new unit types to your fleet. Long range frigates, flak frigates, carriers, heavy cruisers, and support cruisers are all great additions. The Hoshiko, Guardian, Overseer, and Subverter are awesome support cruisers that are well worth your time. Long range frigates are your best damage dealers early game, flak frigates are your best damage absorbers, and heavy cruisers offer a great late-game balance between the two. Light frigates are good at killing carriers and support cruisers.
Keep in mind capital ships are most vulnerable to long range frigates and bombers. Both of these units are countered by fighters. As a result, if you don't have fighter support, your capital ships are very vulnerable to being destroyed by these unit types. This is why carrier-class capital ships are so highly prized in the early game, since they can effectively protect themselves from their own counters.
