Free to play for 3- or 5-days every so often
To be honest, I got this idea from looking at Steam, they're advertising a game called Myth of Empires. The game is free to play for the next 3 days, and I haven't played yet, but it looks good. I would not have bought the game if it cost money, but now that I have a free period to try it out, why not? If I'm not having fun I don't buy it, if I'm having fun, it'll justify me buying the game. This method can only work if your game is good.
Looking at this, I thought about Ashes of Creation and the sub model they're putting forward (which I'm a huge fan of and it's the best win/win for everyone), but I think it lacks accessibility. Imagine if you guys implemented a 3- or 5-day free play period, like every 3 months or so? People who tried it in the beginning and maybe didn't like it, would normally not resub. Even during new content release, some might resub but not all. All of that changes with a free period, the number of people who will try it again, the number of people trying for the first time, all of it will increase, and how many of those people will convert to subs? A lot. Probably a lot more than if you didn't do a free period. It's a great way to bring back old blood and get new blood at the same time. That being said, I think you should do this for the launch of the game, for obvious reasons. I'm not an expert in this field, I just recognized the genius of this strategy from seeing Myth of Empires doing it with Steam. I hope this suggestion helps!
Edit: I want to emphasize because there's been a little confusion. Some people think I meant 3 or 5 days free to play any time someone creates a new account and this is not what I'm talking about. What I'm saying is, I like the idea of a specific time period that is 3 or 5 days that the game can be played for free (Example: December 1st - 5th). In this example, if someone decides to try it out December 4th, then they'd only get 1 day to play for free.