In my current team, I've been able to build a bunch of small applications from scratch. However, I feel like I could have done a better job at planning and designing the code for the applications.
At University, we needed to create a UML, sequence diagrams, user stories and a requirements document for our projects.
None of this has been expected or mentioned by anyone on my team.
Usually, I'm given a ticket with a 3 sentence description of the project. The rest is up to me, and I usually get assistance from people in my team in figuring out the requirements and the system design.
When I get started on the code, I usually work on a small piece of functionality and grow the application "organically". It does feel unorganized to me, as I'm figuring out stuff as I go, having a vague plan in my mind.
What are some practices/techniques to approach the planning and designing of code, before jumping into the IDE?
This is a good example of the gap between the academic world and industry :) You'll find that many of the "proper" ways that you learned in school are completely unrelated to how companies operate.
Rather than a starting point of the UML, sequence diagrams, user stories, etc that you learned in school, start from "how do things get done at this company?"
Talk with managers and TLs on the team and get their input and figure out a system of how to do planning. What you're doing may be fine, but it sounds like you could do more with writing down your process and collecting input from your team. Many places will call this a "design doc".
We have a whole masterclass about this! https://www.jointaro.com/lesson/e9hQDgURiLYZC6l5MBDs/system-design-series-taro-playlists-part-1-what-real-system-design-looks-like/