What you should do, is take an experience from the past and remember how it made you feel.
Examples 👇🏻
Practice: go back to a moment from your past in which you felt confident. We all have at least one moment.
Imagine the experience like you are reliving it right now and really feel the emotion of confidence.
Goal: "Win my boxing match."
Take one experience of success that you are most proud of.
Relive the moment, remember the place, vibe, people around you, how you felt...
Really let yourself feel that winning feeling.
Feel like a winner and visualize yourself winning the fight.
Create a confident feeling, then visualize yourself behaving like a confident person.
That's successful visualization.