I wishlist every game that looks like it has potential; check it every couple weeks to see if there’s any 90% off deals. Pretty much don’t bat an eye at anything below that.
Don’t you get emails when something on your wishlist is on sale?
Alternatively you can set up alerts with isthereanydeal.com
The steam mobile app also gives you a notification when a game in your wish list goes on offer
I have that disabled or blocked. I don’t check my email all that often, and most of the alerts I did get were below the purchase-worthy discount, so it wound up just being a lot of spam.