Remove your plants from their containers. If you see that the roots are circling the plant, or coming out the bottom of the pot, it means your plant is root bound. If it is root bound, you'll need to break up the roots a bit before you plant, so they can grow unrestricted. If you don't the roots can keep growing in a circular pattern and strangle the plant. Some people rub the outside of the roots to untangle them while some are a bit rougher and pull the roots apart. Do whatever suits you - most plants are very forgiving.