1. Spam out as many colonies as you can.
2. Micro the tax rate to keep as many of them at 100% approval for the massive pop boosts from super-breeder, while keeping the tax rates as high as possible.
3. Spam morale buildings so that you can keep taxes higher. Consider getting Xeno Ethics. The harmony crystals and neutrality morale boosts are AMAZING for early game economies.
4. Once you hit the econ wall in the early mid-game, you should have at least 20-30 colonies.
5. Turn tax slider AND spending slider as low as possible. Watch your econ recover quickly due to super-breeder.
6. Once it's recovered enough, turn up spending and taxes and start spamming colonies again.
On large or larger maps, I think this early-game strategy is the best.