Commercial: Aimed at the advertising industry, this displays emotional energy and charisma. It demonstrates your ability to sell a product or brand. The lighting is brighter and punchier, with less shadow.
Theatrical: Geared toward casting in films, TV, and plays. Conveys more emotional depth and range. Can be more focused on identifiable personality types. Tends to be darker, Rembrandt lighting, more moody.
Just as with normal business headshots, you should bring many options to try. You want to wear clothing that will make you feel confident and comfortable. And it should add to the scene or character you are trying to create. And yes, it should be ironed and ready for the camera. Please don't stuff all your outfits in a duffle or wad them up...
Consider what you want to convey through your headshots.
Consider if you have a certain "type" you want to portray if you are shooting theatrical headshots, and how you would describe it.
Consider what ratio of Commercial vs. Theatrical shots you need.
Feel free to share a Spotify or other playlist if you want a certain musical vibe to help you get into the mood.