Here are some tips for scientists on the liberalism line, which is what many people seem to use them for:
- Your first scientist will most likely be able to pop maths, depending how early you get him. I usually don't do this and wait for a better tech pop, or settle occasionally. If you are philisophical you can settle more since you will be generating more scientists. I really only settle when my capital is going to be a research powerhouse.
Once you research meditation + (code of laws OR drama), then you can pop philosphy. This is a great tech because it gives you pacifism (more GPP), and taoism if you get it first.
After philosphy, civil service works well. I'm not saying you research the techs in this order, I'm just telling you which techs you need to research in order to get the next tech that can be popped. After civil service you can either pop paper, or research it manually.
After paper is education. Education takes 2 scientists but it's worth it since you get to liberalism fast.
Next: If you haven't researched machinery, but you have both metal casting and compass... your scientist will research liberalism. This is very handy, since with enough scientists you can effectively pop your way from paper --> liberalism and get the free tech.
This is the general path towards liberalism, and afterwards it doesn't matter quite as much in my opinion. If you don't have the prerequisites for printing press, scientists after liberalism can bulb chemistry (assuming you have gunpowder). I think in acid's demogame, he took gunpowder from liberalism, then popped chemistry and ran over the world with grendiers.
There's a complete list of the great people tech preferences here:
http://forums.civfanatics.com/showthread.php?t=140952
Hope this helps