"One of your feet is in front of the other."; "One foot is in front of the other."
"Your one foot" doesn't work - it implies that the person has only one foot, in which case it can't be in front of the other, which isn't there.
If the two feet were on different levels, "ahead" is not the correct word. You could use "higher" or "lower". One foot ahead of the other is the normal way we walk on level ground.