You can just leave it on and wait for people to watch enough videos on enough of your games to make a difference.
But that shouldn't stop you from trying, because it's one of the most flexible revenue models and it has a long tail. The biggest hurdle with this model is that you need a lot of users to make any significant money from ads. Every time a player watches an ad, you get paid. This is another staple of mobile gaming, and it consists of displaying advertisments to the player in key UI locations or moments in the game. So you never have to stop making your dream game a reality. You can even make games on the go! GDevelop has Android and iOS apps for iPhone and iPad. It still in its development stage, but you can already try it out in your own games. GDevelop has a community extension which makes in-app purchases possible. Incorporate this mechanic as early in the game development process as possible. So, if you're going for an in-app purchase model, be sure to focus on items that do not affect the balancing of your game. Nobody wants to feel like they're playing a game against people who have just paid to win.
The trend at the moment is to exclude upgrades which affect the balancing of the game, and focus on aesthetic items or timers instead.
