Anyone got any popular strategies that are effective. I’ve tried the “special currency” method, where players can buy another currency to help them buy things quicker, which didn’t work out so well.
It’s one of the things i’ve struggled with the most when marketing a game.
I would recommend taking a look at how Fortnite handles things. There’s a reason it’s the most successful game out there right now.
A couple strategies they apply:
Though most importantly, players should feel like they are getting value out of their purchase. Ask yourself, would I want to buy these items? If the answer is no, try to imagine what kind of change/addition would make your items even more awesome.
Also make sure your game makes it easy to purchase items. If players have to actively look for a shop, they are not going to be happy or incentivized to buy anything.
Out of interest, when you say
Do you mean a physical shop on the world or behind a shop button to the side of the screen?
Not a nitpick, genuinely curious 
Well, I have a game, and in the game there is no health regeneration, but there is a dev product to heal very cheap that only costs 30 Robux, this is what more ROBUX has earned in my group, because of the game is so difficult, people buy it many times because they do not want to die. I hope you understand what I mean.
Both,
As a game developer, you have a clear picture of the game’s world, where everything is, all the secrets you put in, and so on. However, the player has to explore all of these things by themselves. Before playing the game they won’t know where everything is. You therefore want to make sure that your game’s shop is not going to be one of these “secrets” for players to discover; You want it to be obvious.
So in the case of a physical shop, you want it to be clear from the get-go where the physical shop is. Lumber Tycoon 2 has you spawn and build near its main shops, so that’s a great method for players to figure out where to go to buy things.
In the case of a digital shop (in interfaces), you want to make sure your shop is not hidden behind 5 submenus, and it should also be clear what the shop is. Usually an icon like a shopping cart or a coin icon with a bit plus next to it are clear indicators. And obviously you will want these icons/buttons to be on your screen often so players notice them, though they should not distract them from what’s important: the gameplay itself.
Also using psychology is one of your best options, like putting many unprofitable products, so that the others look much more profitable. Example:
EDIT: I recommend you see this article.
There’s not really a “best” method for creating microtransactions, every game is different. If you want to insist on finding the “best” way to convert plays into robux, then I would say that the more fun a game is, the more robux you’ll earn from it. If you focus more on making a fun game than the “best” monetization strategy, you won’t have to worry a whole lot about your monetization.
That being said, in my experience (as a player) I’ve found a few guidelines which increase my likelihood of spending money on in game perks.
In general, I find it unpleasant to play games which force spending to remain competitive. The reaction to EA’s Battlefront 2 is a great example of why you should not force progression through microtransactions. Mobile games are the only place where this rule does not apply. Mobile games such as Clash of Clans appeal partly because of a long progression system, and monetization strategies revolve entirely around the “speed ups” which can help you unlock new upgrades.
A lot of unsuccessful games on Roblox fall into this trap. If you constantly bombard a player with advertisements, that player is going to stop playing your game. You may squeeze out a few extra robux from players, but the constant advertising pushes players away from your game.
This has already been said, but it’s something you want to make sure you’re doing. If a player has the option to buy something, but that thing is only useful to them for a small time, fewer people will buy it.
Ideally, your microtransactions should appear useful, but optional to players. If your players see your microtransactions as optional, but they have little use, less will buy them. If your players see microtransactions as useful, but necessary to continue playing the game, you’ll drive away players.
Frequent pop-up GUIs advertising “special offers” or if it were a tycoon, pads that when you step on it it pops a purchase GUI.