Two other things good for the frog kick...one day do a frog kick practice in a place that is maximally silty, and keep looking at your "handiwork" behind you every few minutes, to see if your are leaving a trail....swim close to the bottom to simulate the situation where frog kick will be needed to avoid silting.
The other....get dead neutral and just use mask fins and snorkel....slickest wet suit possible for best hydrodynamics....or just swim suit in pool....get a good breath, go to a depth of a few feet, and practice big frog kick push and nice long glides....Work on max glide, and efficient push....you can get very good feedback for what you do right or wrong, with the ultra low drag of no tank and bc.