The best way to have a good idea is to have lots of ideas.
The always excelent PhD Comics have a new video on detection of exoplanets.
Although they didin’t discuss it in the video an update to the Drake Equation based on the latest data would suggest that the values are:
R* = the average number of star formation per year in our galaxy
fp = the fraction of those stars that have planets
ne = the average number of planets that can potentially support life per star that has planets
fl = the fraction of the above that actually go on to develop life at some point
fi = the fraction of the above that actually go on to develop intelligent life (civilizations)
fc = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L = the length of time for which such civilizations release detectable signals into space