What to do next

Hello, I’m new at this forum and I’m glad to find it. I have been
learning rails in the past months, and I want to go deeper. I have
learn a lot about crud, models, controllers, migrations, actionmailer,
and a little about ActionJobs. But I want to go deeper than that and I’m
having troubles to find a good source of learning. Can someone give me
some advise about what to do next? Maybe a good book name, a free or
cheap course, a good site… anything is going to be welcome. Thanks!