Define your goal(to your self).

Additional pointers, break it down.
Practice grabbing and pulling a mag from whatever retention you would actually use (I use a pocket, if this is for competition, use a mag holder)
Once you get that down, pratice getting a full mag from belly height and inserting it.
Then, insertion-mag release.
Finally, tie it all together slowly.

Use a timer, start slow- like 4-5 seconds. Focus on moving slow and being smooth.
Eliminate wasted motion.
You body shouldnt move.

Once you get that, slowly work the time down.

In a week or so of daily practice, start pushing it. See how fast you can go, but keep in mind, speed is in efficiency.