Now that's the pivot. I reckon one wants a monopoly on high-class planets (therefore surveillance), nearby space resources, very early starports, good research... and the price tag for all this is considerable. Considering that one starts with 5000bc that quickly starts going yellow, and that praying for those "1000bc" anomalies is hardly a sound economic strategy, I think there must be a reliable method for buttressing one's capital early-game, in order to cope with an aggressive expansion policy.
I don't know if you're planning on getting the TA expansion, but it's been tweaked to slightly reduce the effect of the economy crash during colonization. Basically, you get a little less cash to start with, and they're bumping up tourism income as a steady buffer. IIRC, tourism income is related to the percentage of the galaxy you control, so it's independent of population size/taxes. In the TA beta games I've played so far, it does help smooth out the crash a little, but it's still going to be there if you expand aggressively.
There are different ways to cope with it, which makes the game interesting. Some players build extra surveyors, hoping for those cash anomalies. What I do is rush-buy two or three sensor ships (cargo hulls with one engine, and crammed with sensors) to send out ahead of my colony ships and survey the neighborhood. In addition to scouting the best planets, I'm hoping for contact with a minor civ, or one of the main race neighbors, so I can start selling tech for cash. That's my main income buffer for the colonization crash... I'll sell just about everything, since few of the early techs are strategically valuable unless you're playing on a very small map (which I never do) that can lead to early conflict. Any cash anomalies found by my surveyor are just gravy to fund another colony ship. Since I depend on tech trading/selling in the early phase, I make sure to play with at least 3 and usually 4 minor civs in the game. So that's just one approach. And obviously this works best if you're high in Diplomacy skills so you get better deals.
As Dystopic said, you don't need to keep approval higher than 42%, because (IIRC) population grows at the same rate between 42% and somewhere in the 70's, so you might as well milk the population for max taxes, except for the week right before an election when you fake 'em out with a low tax rate to boost your approval.
Apart from that, minimizing the crash is just a question of not over-extending; knowing which planets are most important to colonize, and which you can leave for later and risk being grabbed by an opponent. Sometimes that's a good thing, if you're sure you'll have enough influence to flip it easily. The AI isn't very good about avoiding risky colonies deep inside someone else's zone of influence. So you don't have to grab everything in the neighborhood. It depends on how you've set up the map, if it's a "fast" game on a tiny map, or a longer-term buildup on a huge map, what other races you're facing and their likely strategies, and so on.
