The most important skill for a teleprompter operator is to be a good listener. Always be anticipating / cue to parts of the script that the talent wants to rehearse or edit. If you can quickly be where the talent wants you to be without much hesitation or waiting — you’ll be in high-demand.
Know your software inside / out. Learn all the hotkeys. Practice. Practice. Practice. Having on-set experience does help, but make sure that you’re editing scripts, learning shortcuts and mastering the software. The quicker you’re able to move around the software, the more the end-client is going to love working with you.
Aside from being a software wizard, you have to be a likable person. Always walk into a job with a good attitude. Walk into a job being friendly + confident. Make sure to match your client’s energy and use your on-set skills to know when to chime in / make suggestions and appropriately interact with your end-clients. A lot of these skills are interpersonal and can take awhile to master if you’re new to being on-set or with event crew.