questions about てしまう、てくれる、んです

One big difference I’ve noticed between myself and native speakers is that they end sentences withてしまう, てくれる, and のです／んです A LOT in daily conversation, while I tend to default to plain statements (です、ます)

I understand the meanings of these grammar patterns (or at least I think I do) and when native speakers use them, they make perfect sense to me. But I struggle to remember to use them myself because the way of thinking behind them feels very different from English. I especially struggle with てくれる when I (speaker) don't appear to be the immediate beneficiary of the action.

Another example is ですけど, which I think I understand better and use that one more often.

Does anyone have any tips on how to internalise these patterns so they come out more naturally when I speak?

Cheers.