How to propery pay back goodness and develop gratitude?
I think that a typically Buddhist recommendation is that you try to be &quot;easy to support&quot;. For example if someone tries to do you a kindness (for example, by offering you food), then you're &quot;easy to support&quot; if you accept what's offered without making further, difficult demands.
Another example of being &quot;easy to support&quot; might mean being inoffensive and harmless (although arguably everyone should try to be so anyway, not only when repaying a kindness).
That said, I'm not sure that I agree with the premise of the question (that you should &quot;pay back&quot; goodness). I thought that kindness isn't necessarily supposed to be transactional: for example, monks don't sell Dharma. So when lay people support monks, and monks support lay people, I'm not sure this ought to be viewed as &quot;paying back&quot;.
A fairly widespread (not necessarily only Buddhist) alternative to &quot;paying back&quot; is called paying forward. That means, if someone is kind to you, then you &quot;return&quot; that favour by being kind to someone else!
&quot;Paying forward&quot; is a famous concept, at least on the internet: it's mentioned in one of this site's help topics, for example:

Pay it forward
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As an idea it's perhaps not incompatible with Buddhist ideals.