If you want to evenly space them, it's easiest to alternate between the Arctic and Antarctic. Some people just go to the Arctic twice, near the equinoxes so the visits are almost 6 months apart, but it's not the same.

"Cast Iron Pan", by Randall Munroe, licensed under Creative Commons Attribution-NonCommercial 2.5 License

Alt Text

If you want to evenly space them, it's easiest to alternate between the Arctic and Antarctic. Some people just go to the Arctic twice, near the equinoxes so the visits are almost 6 months apart, but it's not the same.