It doesn't have to mean exactly that by the way, but it should be concise, because I don't want to use something that would be a mouthful.
It's not as incomprehensible as most idioms, but there's always
break (up) the routine
Or from the idiom "stuck in a rut", there's
break out of the rut
Both of those are based on already having a routine where you're always doing the same thing, and stopping doing so. For that case or cases where you're trying to avoid that there's:
shake things up
That's a one-off, but you can always commit to:
keep shaking things up
I imagine I've barely scratched the surface, but it's some thoughts to be getting on with.
We do have the expression, "in a rut" which is pretty much the opposite of what you want to say. If someone is doing the same thing every day and not switching it up, we might say, "he is in a rut," or "he got into a rut," or maybe "he's been in that rut for a long time."
A rut is the deep track that someone's wheels have dug into the muddy path, and if you get your own wheels into it, it's hard to get out.
So for your meaning, you could negate that expression and say you want to avoid "getting into a rut" or you want to "stay out of that boring rut," etc.
One idiomatic expression that comes to mind is...
ring the changes
- to do something in a different way in order to make it more interesting
Ring the changes on packed lunches using different types of bread and spicy fillings (Cambridge Dictionary)
This phrase derives from the practice of bell ringing. Each pattern of the order of striking the bells is called a change. In order to 'ring the changes' all the variations of striking pattern are rung, bringing the ring back to its starting point.