I mostly don't try. I went over my friends list, stopping on the ones I hear from actively or run into a bit still around here. I have it about 40-14 right lean from that group. Many I knew from declarations and arguments, like bybee.
I figure most people know their own inclinations and are pretty up front about it. If I think someone leans outside of the declaration I tend to suspect my own litmus in play. I've found that people who declare more/than tend to move about more issue by issue than people who declare Right or Left with the add ons.
Or it could just be you trying to act as arbiter of what's to the right and if you're at X then you're bias will tend to see that as the starting point where the guy to the left or right of you might mark it on their X and see you as either a little to their right or suspiciously liberal.