Ask HN: How to improve career once established in my job?

Hello everyone! So I'm trying to get ideas on how to improve my software engineer career given that I am well established in my current job.

How have you personally done this? Can you give me any tips/ideas?

I am OK spending some of my personal time doing this, I just don't know exactly _how_ to do it? Is it blogging? Working on some personal projects? Open Source?

Thanks!