List the criteria needed for the fight scene. This list should include the length of the fight scene, style of fighting, actors involved and the setting for the scene. If the fight scene is on a stage or film, a couple minutes is generally the length of the fight scene unless it's an important scene for the flow of the script. The style of fighting could be rough, such as a bar or street fight, or skilled and structured like in classic martial arts films; there may be weapons or protective gear depending on the setting as well.
Research all necessary elements to make sure the facts are correct. This is especially important for fight scenes in novels, because the words alone must convey the scene. In film or plays the actions will be scrutinized by the audience if inaccurate and the actors will struggle if the moves are unnatural. If weapons are used, the weapons should be carefully researched as well.
Determine the key points in the fight scene, and how it will end. Key points will be where one actor gets the clear advantage or where the advantage shifts from one actor to the other. The ending is important because fights don't just dwindle, there should be an ending blow to signify the clear end to the fight.
Consider the actors in the fight scene and adjust your key points, ending blow and camera or stage direction to accommodate the actors. For example, if the ending blow is a left hook but your lead is right-handed and his left would be toward the audience, it might be best to adjust to the right hook instead. You want the action in clear view of the audience as well.
Use the actors to create the fight scene choreography, having them run through various moves at extremely slow, controlled motion. This will allow you to capture the effect for written description and to determine if the moves are the most effective and entertaining. If there is ad-libbing in the fight scene, be certain the actors can pull it off naturally; awkward ad-libbed jabs with poor timing can throw the audience off.