I usually don't tax my colonies at all on the first few turns of my game. The thought is that if I hold off taxing, then approval will be 100%, population growth will double, and my revenue base will be larger when I do finally start taxing. I ran some numbers through a spreadsheet and came up with the following:
Initial conditions: 500 Million colonists
+100 Million colonists/turn under 50% taxation
+200 Million colonists/turn under 0% taxation
If I leave taxes at 50% for the first 45 turns (the time it taskes to reach 5 Billion population, the normal population cap), I make a total of 45bc for those 45 turns (I'm assuming that the tax equation is TAX=TAX_RATE*population, I couldn't actually find this equation anywhere...) If I put tax down to 0% until the population reaches 2.5Billion, then jack it up to 50% again, I make 56 BC over the same 45 turn period. Thats an improvement of about 25%. So, its in your best interest to set tax to 0% until your average planetary population has reached 2.5 billion.
--Brad
