Quick Run Down
Depends on the tier you use him in, but regardless of the tier it's set is almost identical every time. I will split it up into tiers based on Smogon Singles.
In the lowest tier it's available in, it functions as the tiers second fastest pivot, only losing out to Mega Beedrill by a measly but important 2 base speed. It is commonly used as a specially based mixed pivot and it's overall stats are fairly good for the job, but mediocre for doing serious damage to bulkier mons.
It's time in OU was spent doing really the same thing as it now does in UU. Though the thing is, OU has another Pokemon in the tier that arguably does everything Zeraora does, but better. None other than Tapu Koko. Koko functions almost identically to Zeraora as a pivot. The thing is, Koko has options. While it lacks the amount of punch that Zeraora has, it makes up for it in it's signature ability to summon electric terrain on every switch in. Koko also gets blessed with a better defensive typing with it's additional fairy type. The most important thing however is that, it's movepool is so much better for a pivot. Defog allows it to clean up hazards, screens allow a nice boost to the teams defense, roost gives it reliable recovery, nature's madness gives it guaranteed damage when it needs to do some, and U-turn while slightly less powerful, is guaranteed to hit every type and not be stopped (unlike volt switch versus ground or electric absorb abilities) effectively allowing it to pivot no matter what. Also, it's important to know the difference in speed is hardly notable in this instance. Quickly I'd like to add that it also has competition with Tornadus-T as a pivot aswell. So yeah, if you're in OU, I'd recommend using Koko instead.
Simply put, it's not viable and really shouldn't be considered. Where 143 base speed is a blessing in all the other tiers, you enter Ubers and none of that matters anymore. You enter a tier where Zeraora's attacks will hardly be denting anything. Where a Pokemons ability to setup and sweep is what makes it good. Earthquake and Earth Power are very common moves in this tier and almost every Pokemon in it can learn one of the two. Damaging pivots like Zeraora won't do anything, the damage output is too low and it will often die off one hit from most things in the tier. Now, a bulk up set does exist in every tier that I didn't mention until now, and that's because of its weak defense stats making it hard to pull off. I think it's only reasonable to bring it up now because it's the only way it will even have a sliver of a chance to succeed in Ubers. If you can SOMEHOW manage to get 3 bulk ups in, you can manage to sweep with this mon, and even then, it's not guaranteed since of the bulk and typing of some Pokemon allow them to just win the matchup regardless. Example being Giratina-O being able to soak anything it can dish out and just roar it off the field or drop a Draco which will clean things Zeraora up swiftly.
For the simple answer, don't use it in Ubers, like ever.