Velocity, Velocity, Velocity
For about 10 years, we were doing very stupid things across games: we didn't allow players to re-queue after a session ended. One of the secrets to Battlefield's success is that it puts you on a server that keeps playing the next match, leading to incredibly long session times I haven't seen in other titles.
For reasons beyond me, only in the last couple of years have we seen other games start to adopt this. First it was Apex Legends, then Overwatch. If you are a developer reading this right now and you don't have this in your game, you should implement it immediately. I'd love to show you an A/B test validating its value, but first, you need an A/B testing engine. One day, HD games. One day.
The place where this has the most impact isn't shooters, but games where there's a direct connection between engagement and monetization. In many ways, this has been the secret of slot success: they're able to tune velocity extremely high. It's not just that bet size is variable; the sink speed is high as well. This lesson especially applies to Match 3: less time in the meta, more time matching. When you finish a game, stop returning players to the home screen; move them directly into the next match.
Any game, even those with energy-based monetization, should be using this well. That includes 4X games with consumable troops, where the model should focus on getting players into battles ASAP, burning troops, and getting them to re-queue. Even in games like Magic: The Gathering, one of the smartest moves was introducing Quick Play Draft instead of real-time drafting. Clash Royale is missing on this, with Mega Draft, which takes far too long. They need to set a time limit for choosing a card using a chess-like clock. The same is true for real-money or ad-based games, where the margin increases with the number of games played. Velocity, velocity, velocity.