Here's my early game strat.
On my first turn, I buy a factory on my home world and begin building a second, followed by two or more research centers. I begin scouting near-by star systems with my survey ship, and colonize a habitable planet with my colony ship. On the new colony, I buy a factory, and, since the nearest planet is usually class 4 or 6, I make it a "research planet". I might save a tile or two for other uses, like an embassy or entertainment network. I then buy another colony ship at my homeworld.
On my second turn, with any luck, I've found more habitable planets nearby, and I send my new colony ship towards them. If I've found multiple habitable planets, I buy another colony ship. Otherwise, I let my starport build it until I do find more habitable planets.
I keep this strat going until I run out of money. Most planets below class 10 become specialized worlds. If I need a starport in the area, I make it a manufacturing world, otherwise I make it a research world. On my class 10 and above planets, I buy the first factory, if I can afford it, and immediately build another. I might build a starport next, or go straight into building research centers. When I run out of money, I cut my spending back to the break-even point, and wait for my economy to catch up.
Using this strat against "sub-normal" intelligence opponents, I'm way, way ahead on everything - research, economy, population, influence. I don't start building military vessels until someone else does, in order to keep research and social production going as strong as possible and avoid ship maintenence from bankrupting my already fragile economy.
I hope that helps.
