The phrase personal brand puts a lot of people off, and reasonably so, because it suggests performance rather than substance. A more useful framing: your reputation is the short sentence colleagues use to describe you when your name comes up. You cannot control it entirely, but you can influence it considerably, and it determines which opportunities reach you.
Decide what you want the sentence to be
Pick one thing. “The person who makes messy projects work” or “the one who actually understands the billing system” or “the person you go to when a customer is angry”.
A narrow reputation is far more useful than a broad one. People remember specifics and forget generalities, and opportunities are routed by specifics.
Make sure it is true first
Reputation built ahead of capability collapses on contact with a real problem, and the collapse is remembered longer than the original impression.
Choose something you are genuinely good at or genuinely committed to becoming good at, then make it visible. That order matters.
Do visible work, not just valuable work
A great deal of important work is invisible: preventing problems, fixing things quietly, supporting others. This work is valuable and it does not build reputation on its own, which is an unfair but consistent feature of organisations.
Balance it. Ensure that some proportion of your effort goes into work that has a visible output and a name attached to it.
Communicate results without bragging
The distinction is simple: talking about the work builds reputation, talking about yourself does not. “The migration finished on Friday, here is what changed” is information. “I worked incredibly hard on the migration” is not.
Short factual updates, shared where relevant people will see them, do the whole job. Credit others genuinely while you do it.
Be consistent, especially when it is inconvenient
Reputation is built from repetition. Being reliable four times out of five is remembered as unreliable, because the exception is the memorable event.
If you say you will send something by Thursday, send it by Thursday or tell someone before Thursday that you cannot. That single habit builds more reputation than any amount of visible achievement.
Be useful to people outside your team
Your manager knowing you are good is necessary and insufficient. Opportunities frequently come from adjacent teams, and they only know you if you have helped them or worked with them.
Answer questions from other departments properly. Turn up to cross-team sessions and contribute. This is the entire mechanism by which internal moves happen.
Handle mistakes in a way people respect
Everyone makes them. What is remembered is the response. Naming it early, saying what you will do about it, and not repeating it converts a negative event into evidence of reliability.
Concealment does the opposite, and it is almost always discovered.
Let it work outside the building
Your reputation is not confined to your employer. Colleagues leave, join other companies and get asked whether they know anyone. That is how a large share of hiring happens, and it is why treating people well matters commercially as well as ethically.