Like conditioning to a clicker, "Eyes On Me" is more of a training tool than it is a trick in and of itself, but it can be incredibly useful. Foxes have the attention spans of gnats, so it's helpful to have a way to quickly redirect them to looking at you when they're starting to get a bit off-task.
Prerequisites: For this trick, I assume that your fox has already been conditioned to a training clicker.
I've heard people use a lot of different commands for this, everything from "Watch me!" to "Pay attention!" I prefer to use "Eyes on me!" because it's a phrase that is unlikely to come up in conversation. That way, every time you say "Eyes on me", it will be when you are trying to get your fox to look at you. Otherwise, every time you say "watch me" to someone else, your fox will look but get no treat, and the command will weaken over time.
Hold a treat out so that your fox can smell it, then slowly raise it so that it's at the level of your eyes, saying "Eyes on me". The instant your fox makes eye contact, click and reward. Rinse repeat multiple times a day with multiple treats per "session", making sure to only click when your fox makes eye contact.
After a few days of doing this, stop using the treat to "lead" them to your face. Just approach your fox and say "Eyes on me". If they look at your face at all, click and reward. Once they're consistently looking in the general direction of your face, start to only click and reward if they make eye contact.
Over the period of a few weeks, your fox should make eye contact whenever you say "Eyes on me".
Troubleshooting: If they immediately look for your hand instead of your face, it means they've misunderstood the concept. This is a pretty easy fix. Next time, hide your hands behind your back before saying "Eyes on me" again. If there's no hands to look at, the fox will generally look to your face in confusion as if to say "What do you want?". The instant it looks at you, click and reward.