There are two keys to bottle-flipping. One is getting just the right amount of flip on the bottle. (For that, keep practicing!) The other is filling the bottle just 1/3 full. That leaves the water free to slosh around, and it absorbs some of the bottle’s motion energy, slowing its momentum and making the bottle bounce less when it lands. With less forward spin acting on it, the water flows to the lowest part of the bottle, and gravity pulls that mass to the table. It is more stable upright than a full bottle when it lands because a larger portion of its weight is lower.