But while I do think appreciating what you have is part of how to avoid the hedonic treadmill, I don't think it's a matter of learning to be happy with a routine.
I've found it possible to make a conscious effort to avoid hedonic adapation, and enjoy novel things without allowing them to become a new baseline. If you can maintain your expectations at the same level, while improving your actual circumstances noticeably above that level, you can maintain a higher level of enjoyment of your life.
So the goal is generally to increase your level of happiness - to have a higher baseline in terms of feeling good and having a sense of well-being.
It's futile to chase joy in place of happiness, because each hit of joy makes the next one feel less exceptional.
Although joy feels like happiness, it's not the same thing, and it's barely related. Joy often has to do with doing more. Doing something extra and exceptional to move the needle.
Happiness often has to do with doing less. With being less focused on doing/attaining/obtaining something new, and more focused on mindset: on finding happiness in what we already have.
In any case, I'm not claiming a universal recipe here, just observing something that seems to have worked well for me.
To give an extreme example, someone who's addicted to drugs might receive extreme joy from their next hit, while at the same time being deeply unhappy, and unable to take joy from anything else. That's the hedonic treadmill at the extreme.
At the same time, someone who's very happy might be able to take joy from something simple - like a fried egg yolk with the perfect consistency - because their mind is not preoccupied with seeking bigger and better joy, they may be more free to find it in simple places where it arises naturally.