Don't spend your gems on double share, I did that mistake before but now I just sell my company very quickly to get shares, it's way faster than trying to get a lot of shares at once.
I'd say save your gems for multiplier and if you're near the next tier wait until you cross it before buying multiplier since you can get some with the event and wheel.
And there's a trick to improve your odds of success in the event, record the shuffling and then replay frame by frame, it's possible to see where some of the cards went. It's not 100% accurate but it helps quite a bit.
While I'm at it, another nice trick (I'm on pc, no idea if it works on browser/mobile): when discovering a new decoration, wait for the auto save then discover it, if it's not what you want quickly close the game and you can retry