One thing I noticed about this game right away is that the difficulty settigs are poorly implemented. If you've ever looked at...say, Civilization 4's difficulty settings, you'll see that on "easy", the AI researches/builds/colonizes slower than the player. On "normal" everything is even, and on harder difficulties the AI can produce all these things faster than you can. This is not the case in Sins, so as a newbie trying to grasp the basics of the game, you'll eventually find yourself overwhelmed by huge fleets of AI ships. Here are a couple of things I've learned to make the game newbie-friendly:

First thing, browse to the game installation folder and look in the subfolder named "Gameinfo" for a file named "Gameplay.constants". Copy and Paste it on your desktop or some other place you can keep it as a backup. Open the original using Notepad and scroll down to the bottom where you will see a category named "playerAISharedDef". Here you will see such things as "table-Aggressive/Defensive/Research/etc". Notice that under "table-Aggressive" the first line is Buildship 10. These numbers are a "weighting" of what the AI will do with its money, and how often. As you can see from the numbers, an Aggressive AI will build ships more than doing anything else. By changing these numbers you can effectively control expansion rate of the AI players. Try changing the Buildship numbers to 3,2,2,2 respectively and you will stop seeing huge fleets attacking you after you've only had time to colonize 3-5 planets in a large/huge map.

Secondly, when setting up the game, make Pirates inactive and click on the insignia's to the far right to make all AI players "easy".

The very first thing to do when you start a new game is to construct a capitol ship factory and your first capitol ship. Then construct the metal and crystal extractors. Build a scout ship and start exploring all the nearby planets. Send your capitol ship to the most weakly defended adjoining planet and destroy 1 or 2 defenders then retreat to your home planet to allow your ships shields to recharge. Rinse and repeat until you can colonize.

Lastly, don't worry about completing missions for AI players. At first they all want money/metal/crystals, which you can ill-afford to give away. Later, they will ask you to destroy either ships or structures of other AI races. This will happen anyway as you begin to expand and fight other AI ships, as well as take over their planets. I've found that ignoring the missions and just playing the game will eventually get me some AI allies anyway, usually ones that dislike my neighboring AI enemies.

I've found a huge difference in the game as a new player when doing all this, especially modifying the "Buildships" info. Eventually you'll want to bump the numbers back up (slowly, probably) to increase difficulty.

Oh, and here's a tip tha has nothing to do with gameplay, but allows the game to load faster and removes the Universe and "floating camera" from the game's initial Menu area:  Explore to C:\Documents and Settings\~username~\Local Settings\Application Data\Ironclad Games\Sins of a Solar Empire\Setting folder and open the file user.setting with Notepad.  Change: GS_CREATE_GALAXY_FOR_FRONTEND TRUE to GS_CREATE_GALAXY_FOR_FRONTEND FALSE