First, jumping with both legs isn't "improper", it's just not ollying. There are situations where popping is the proper thing to do.
Second, can you ollie better when you're not moving? I personally find it easier to ollie when I'm not moving, becuase when I'm moving I'm hesitant about throwing my weight onto my back leg. If so, that's just practice.
I told my kids, "Someday, you'll have kids of your own." One of them said, "So will you."
-- Rodney Dangerfield.