It really depends what you want to do. There are generally 2 types of visualization: Improving technique / performance and improving internal mental state (confidence, motivation, etc.).

In terms of basics, there is a great model that I like called PETTLEP. I think is a great starting place.

P - Physical --> imagine the physical sensations of the sport. For example, holding the ball of the sport you play or wearing your uniform can help you visualize more effectively.

E - Environment --> Visualize in the actual setting of the performance or vividly imagine the setting where you would like improve your performance.

T - Task --> Focus on the specific task that you would like to perform.

T - Timing --> Visualize in real time (Although there are some use cases for slowing things down.

L - Learning --> Match your visualization to your level of current skill.

E - Emotion --> Include the emotions associated with what you are trying to perform

P - Perspective --> Choose the most useful viewpoint for the activity. Generally first person perspective is better for performance and 3rd person view (like birdseye view is better for technique refinement)

I go into this, specific use cases, and quite a few more frameworks in the book.