Haha, no problem, but it's mostly just practice. The key thing seems to be recognizing that there's anything worth picking out in a piece of art to begin with—those with little practice don't notice it anywhere, or else will see it everywhere because of course it's possible to bullshit deep themes into an average episode of NCIS if you're so inclined—then questioning why for various decisions. If you're not sure what something means in a thematic or thesis sense, look at which possibility or possibilities go best with the rest of what you've seen (or read, or heard—works for books and music, too).

FWIW I find most of the rest of Black Mirror a lot less rich than Fifteen Million Merits, though I like most of it. I couldn't write as much on most of the episodes as that one, because I'm just not sure there's as much there. Most are a fairly straight route up to usually some kind of twist, with a little worth saying about the relation of the twist to the rest but mostly what they're up to is pretty on the surface. Nothing wrong with that, and that fact that it consistently tries to say anything at all puts it above most TV, so far as that goes.

To expand a little into other episodes, though, to give some more idea of what I mean by asking why about choices creators make in art: take The National Anthem, for example. When a Certain Pivotal Scene (you know the one) happens, the creators could have depicted it several ways without changing the actual story. A few possibilities: 1) actually show it, entirely, 2) show it but crop out the worst of it, 3) keep the camera nearby, say on people in the room or in the next room over, or on the fictional production crew "shooting" the event, 4) any of the above but show only a little and cut away, 5) just skip straight to after, don't have any footage that takes place during it at all, among other options. There was a choice to make, and the one that was made isn't exactly revolutionary, but also isn't one of the most obvious ones: keep the camera going for all of it (or maybe just most? I can't recall for sure) after showing us every moment at the scene of the event leading up to it, but only show the faces of people watching it on TV. Why? It wasn't the only way they could have avoided putting the event itself onscreen, why do it that way?

Showing people watching a screen, especially something sensational that's been teased from the very first scene of the episode, and holding the camera on it that long does a couple things, I think: in the general case, it invites identity with or comparison between the real life viewer and the viewer in the show; in this particular case, I think the show is also delivering on a kind of implicit promise of horrible spectacle by showing us the most disgusting thing that's happening in that moment, by the creator's judgement. Anyone watching the show, even if they hope the event won't happen or that it won't be depicted at all if it does (which is hopefully most people?) was still held in suspense and to some degree entertained by that will they/won't they dynamic. The result is that this choice both casts judgement on the viewers-in-the-show and prevents the real-life show watcher from casting them as Other and distancing themselves from those voyeurs. This option was chosen by the show's creators because it conveys a message different from what others would have (most of the other options above wouldn't convey much at all, without some further effort, but would advance the plot just the same) and does so effectively. That single choice causes multiple effects on and messages to the viewer, working toward one end.

To take that a step further, both reinforcing the likelihood that this was intentional and possibly adding insight into other episodes, the show repeatedly returns to themes along these lines, of the viewer-as-complicit. White Bear's a huge one, obviously, featuring punishment essentially for the act of watching a crime (and filming! The show also loves to jab at itself and its creators pretty viciously, as Fifteen Million Merits manages to also do in addition to everything else) with a kind of Greek hell of... having crimes done to them while "normal people" watch and record, which is called justice. A couple others tread similar ground—Shut Up and Dance, notably.

Moving into more tenuous territory: Jan Junipero may also be doing something like this, forcing the viewer into more direct confrontation with some message in it by identifying them with some element of or character in the show, at the end, just a bit. The long sequence of server farms and robot arms at the end definitely adds a sense of melancholy and unease over the happy ending and neatly reframes our own emotions about the episode, which is probably the main thing it's intended to do, but that also looks an awful lot like any modern-day server farm. Like where Netflix episodes come from. Like the episode you just watched, finding temporary joy in this fiction while sitting, apparently lifeless... and oh look it's suggesting another show or movie, how nice, this could just go on forever, couldn't it? And that's the season Black Mirror transitioned to Netflix, I'm pretty sure.

That's quite stretch from the pretty clear use of those themes and mechanisms in other episodes and I wouldn't say I'm anywhere near as sure of it as some of the other stuff, since it's pretty abstract and there are other, stronger ways to explain why the scene is there and why it looks the way it does... but then again Bandersnatch came out a few years later and hits some of the same notes explicitly, which makes it just a tad less likely that that wasn't on the creators' minds when they decided how the end of San Junipero should go, and a little more likely that that connection was intended.