An extremely important aspect of imagery is physical / physiological nature of visualization. It is not entirely different from physical practice in that you can have similar physical sensations. Thus striving to physically feel the movements and muscles you will be using while performing is part of it.
The visualization should be as real or close to the actual environment you will be competing or practicing in. If you can be in the environment, the gymnasium, rink or pool that is preferable. Otherwise do your best to get pictures or even video footage of the places you will be competing and aim to see yourself in that environment. As you think of yourself in the environment, tune into sounds as well.
Your visualization should be based on a specific task or component of your performance. You can break a skill down into the components you need to improve and picture those improvements. You can then integrate into the whole sequence for an overall feel. The goal is to get to a place of automation with skills and plays.
The timing of your visualization should be equal to the actual timing of a skill or performance. This includes and can be enhanced when you think of the rhythm and cadence of your movements and rehearsing those to their fullest extent.
The content of your visualization should largely be based on your current level with a particular skill or play. Update your visualization as your skills progress
Visualization will be more effective when you incorporate realistic emotion into the visualization. Recognize in the visualization the energy of the environment you will be competing. It may be an exciting or a quiet environment. Picture yourself performing with the emotional qualities you want in that environment. You can aim to see yourself responding with composure and positively feeding off whatever the energy is.
This refers to whether you are visualizing from an internal or external perspective. The internal is seeing what you would actually be seeing, as if a camera is on your head. The external is the view as if you are seeing yourself on camera. It is generally good to try to see from both perspectives. The external view helps with picturing your form. The internal perspective helps creates realness.