The biggest impact I've had at the places I've worked have been about procedures and methodology, not how to use UML or draw a dataflow diagram.
- Have a process around software releases. Doesn't matter what as much as it has to be repeatable.
- Review your designs, review your code, don't do things in isolation.
- Have a known location for documents and project information.
- Be consistent, don't do every project completely differently.
- Get data before you try to fix the problem.
- Learn from your mistakes and adjust your processes to that learning.
- And many more things that sound like common sense (and they are) but you'd be amazed at how even in 2023 many companies are developing software in complete chaos, with no discernible process.