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 also see lots of people not shift there weight forward much first. So the weight shift backwards is not as dramatic. Which ends up being a very small pop.
Other thing I see a lot is people trying to throw their weight back, but they are very straight legged.