Hire someone experienced to get it through listing
That is, UL listing and FCC cert, as well as CE, RoHS etc. This is a very difficult area fraught with tricks and traps for the inexperienced. They’re not trying to fool people; they just haven’t done a very good job making the process accessible to hobby builders. You cannot solo this; those who have tried have been eaten by the system.
Keep in mind a big part of it is your factory manufacturing the items. You need a factory the listing agency has a relationship with. Random Chinese factory, or even random American one, may not be up to snuff. That’s especially true if your factory generally does limited run stuff e.g. for industrial controls, and doesn’t do consumer products.
It works better if your expert is in the loop starting early
A lot of people think this compliance is a last-minute bolt-on; one of the boxes you tick right before production.
That’s not the best idea, especially when you’re dealing with RF. You are better off having the Code requirements inform your design choices from the moment your idea hits the back of the napkin.
Watch what your competitors are doing
A lot of people see their competitors swerve out of their way to take a particular approach. They think “Well that is weak, I can do better than that!”
Then, as you get into the process, you find out there’s a reason they took that approach. The reason relates to the product safety standards or Code requirements everyone must follow.
For instance there’s a little detail that UL must approve both your device and its installation instructions. Home power monitoring systems like Sense place their “box”, its power supply and all the current transformers entirely inside the service panel, with nothing but a WiFi antenna sticking out. Any half-competent EE can get the idea to mount the box externally with an atttractive, interactive display, and just run the CT pigtails into the panel. But that cannot be installed legally, so UL will never approve it.
UL needs electrical equipment to meet published safety standards (the UL White Book). But UL also approves the labeling and instructions as part of the UL Listing (which is why some instructions are so ghastly; they used tired and true boilerplate text). UL needs to see that the installation procedure is compatible with the Electrical Codes (CEC for Canada and El NEC for most of the rest of North America, for instance). Your instructions can't tell people to violate Code.