When you review a PR from a senior dev, find something improvable, suggest it and the dev updates it accordingly.

The first time when this happened made me the luckiest guy. It's still rare, though.

Even senior devs can learn better ways from juniors.

When I first joined my current company I had good knowledge of CloudFormation and one thing that the company was trying to build in Scala could be easily done in CF, but because I was so new I was scared to suggest changing because I thought they'd know about it and chose Scala over CF.

I learnt better and now we use CF for everything related to AWS infrastructure