There are a few ways to look at this based on where and what you you are wanting to do. I think there is a two-facet approach here where you go both wide and deep. I would suggest to any aspiring technologist that you look at gaining general knowledge and understanding in a broad range of technologies (e.g backend development, frontend development, database servers, server configuration, networking essentials, scalability strategies, security, etc.). At the same time, find a technology stack that interests you and got deep on it.
For new developers in the web space, I recommend looking at the Node.js ecosystem along with the frontend frameworks that exist there (e.g. ReactJS, Angular, Vue, etc.). This has some key advantages:
- Helps develop an understanding of server configuration, security, network protocols, and routing
- It's VERY marketable right now