Build Something From Scratch
For many software engineers, most day to day work is adding features or fixing bugs in an exiting application. The number of times that you'll create a brand new project and launch it for the first time is pretty rare in a lot of jobs, but it's still good to know how to go from nothing to a functioning application (whatever that means for your technology of choice). For example, if you work in a 10 year old Rails monolith, take a bit of time to run
rails new and create a little project for yourself.
Going from 0 to 1 with a project will force you to understand parts of an application that you may have taken for granted and what went into making the non-trivial applications you might work with day to day. You'll get a better feel for what interfaces come with the language and/or framework you work with VS what might have been built in-house. Also, it might come in handy when you're interviewing for jobs and they want you to build a take-home project or a quick coding challenge. Don't be a web developer who can't build a website (or whatever the equivalent is for the type of software you want to write).