1. Work through some books that dig deeper into technologies you already know. This will help you re-familiarize without being too simple. For RoR, I would look at Ruby Under a Microscope, Rebuilding Rails.

2. Just write code. Get back into thinking about different approaches, and explaining the pros/cons of each. Some of this could be leetcode style for interview prep(advent code starts in a few weeks). But also just building apps in Rails. If you don't have any ideas, just go through the standard "build your own X", where X could be twitter, instagram, reddit, etc.

3. Review your resume. Go back to thinking about what you did in your last job. It's likely, with a break, that you can't easily remember what you accomplished at previous roles. If you start thinking ahead of time you can work to recover some of those memories. Start building the stories around them so you'll be ready for the "tell me about time that X" questions/discussions.

Build things. Write your own software to solve real personal problems you have.

I am currently working on a Nodejs web server and docker container management dashboard. It’s just for me and my household, but it scales in ways other solutions I have tried don’t. I have been doing JavaScript work for almost 20 years and I am still learning things and improving my architecture. I know I can do things many other developers cannot because of my years of personal practice and I also realize I am still learning.

Use your existing knowledge to learn (based on data) in-demand skills.

You should do a value/time trade-off first. Figure out the “low hanging fruit” and learn them. Ie learning Docker is much more valuable than learning to become a ML Engineer :)