Depends on the situation. I've been finding a good combo in BtS by being able to get democracy w/ liberalism, then start a golden age so that I can make the free speech/free religion/emancipation/universal suffrage jump for free, and often can get economics for free market before the golden age is out.
I wouldn't put it off any more than to get democracy- A CE gets such a huge boost to towns w/ Printing Press & Free speech and the 10% science from free religion that to put it off would be silly. SE's probably can put it off for a little longer unless they don't have constitution, espescially since they would want to run Pacifism.
Usually I'd get it once someone gets education, just to not take any risks. I've lost it acouple times in the past trying to get greedy. Good techs are anything on the nationalism/constituion/military tradition branch, while printing press is good if you want to snag liberalism real early.