If your going in a circle to the left (counter clock-wise), it should be on the left lead. Circle to the right (clock-wise), right lead.
The front leg that's "reaching" forward more is the lead leg. When you first start out, it's easier to just take a peek and see if you're on the correct lead.
After you do it a while, you can feel it. Your inside hip/leg will feel like it's moving forward more.