Simple, but it requires a bounce per futebol between touches, maybe even two bounces between touches per foot.
We like using a Brasilian Futebol because it has a nice bounce to it.
Focus on the left foot controlling 1 futebol and the right foot controlling the other. Try to stay foot/ball specific if possible. Touches should be belt or hip high to give the futebol a chance to bounce adequately allowing the juggler a time to touch the other futebol. Try to allow only 1 bounce between touches. Ideally the juggler should establish a rhythm which is accomplished by juggling both balls at equal heights, allowing only 1 bounce between touches, which would translate into equal timing of bounce-touch and therefore a steady pace or cadence of footwork.
Sound impossible? I’ve seen it done, just takes focus, skill and practice.