What is something small you can do every day to greatly improve your relationship?

I dunno about “GREATLY” improve, but:

If it’s true, tell your partner “I love you”, quietly and a bit randomly, and mix up the ways in which you tell them. Cut a sandwich in the shape of a heart. As part of a silly note in a lunchbox. Just wandering up to them and hugging them from behind and saying it.

Might be out of place when a relationship is just starting – then it’s kinda clingy and off-putting if overdone.

But once things are humming along, it ticks all the boxes.

It’s small. It’s very little effort to do every day thing. And I firmly believe it makes a difference as relationships mature.