Read the Forums
Which forums do you suggest for getting population reads?
Anything specific for PokerStars?
Twoplustwo is the obvious first board that springs to mind due to it's sheer size.
Be sure to be only looking at the sub-forums that are relevant to the limits you're playing when trying to get a feel for population reads.
Reading MSNL posts when you're a $5nl player might be useful in a lot of ways but won't be at all useful when looking for microstakes population reads.