Simplest option is to follow their prices and buy/sell accordingly. For example I personally believe that USDT is a scam token and I do not trust it a single bit. However recently it dropped like crazy and it worth like 95 cents or so for a while. Well we all know it is tied to 1 dollar and it should not be more or less from it as close as it gets. So I did what anyone with some logic would do, buy it at those prices for guaranteed profit.

Who would say no to something if you tell them something 95 cents will be 1 dollar no matter what, this is guaranteed money we are talking about, everyone would buy it. Now I am holding a bit of it and sold some of it (some places returned to 1 dollar, some places declined to use it etc) I think if you want to profit from stable coins just put a buy/sell order, whenever its low buy it, whenever it reaches to what it should be sell it. For example 97 cents to 99 cents in USDT is smart.