Four words - "100% Approval" and "Tech Whore".
Approval: It will make you grind your teeth in frustration, but keep tweaking the tax slider every turn to keep your approval at 100% from the first turn of the game. This will double your population growth, resulting in more taxpayers created earlier in the game. Keep this up until your home world is just about full (16 billion) before you start easing the slider up. As you increase taxes, use the colony manager to check that your other colonies remain at 100% until they are nearly full, as well.
While you're doing this, try moving the tax slider up until you're in the green and note the difference in income between that setting and the 100% approval setting. It's not as big a difference as you think, especially early in the game.
Sell EVERYTHING: Especially to minor races, who will happily fund your debt until you're on your feet economically. When you sell techs to one race, make a note of what you sold them and make the rounds on that same turn and sell it to every other race, too - your monopoly will not last long, and you might as well get the $ from it while you can. Sell your diplomacy techs, weapon techs, logistics techs, everything they will pay you for (there are a few, like colonization techs, that nobody will buy for the first couple of game years). And sell them one tech at a time, tech values decrease the more items you put into one sale.
Another thing that will help is to turn some (I do about half) of your planets into pure moneymakers. Build one or two factories to help get everything else built, then one farm, one entertainment building if you want, then fill the rest of the tiles with econ buildings. Don't even build a starport. This is the best use for all PQ 10 and less planets, IMO.
Also, if you're going Evil, make sure you tech up to Concepts of Malice and build the Mind Control Center ASAP - it gives an undocumented 100% econ bonus.
There are some true masters out here who could no doubt offer many refinements to the above, but that should get you started - good luck!
