How to actually remember a friend's pronouns, not just mean to
Your friend told you their pronouns changed, and you meant it completely when you said you'd use the new ones. Then a week later you're telling someone else a story about them and the old pronoun comes out of your mouth before you've even noticed, and you spend the rest of the conversation quietly furious at yourself. This is a strange, specific kind of frustrating, because it has nothing to do with how much you respect the person and everything to do with how memory actually works.
The slip is not a belief problem
By the time a friend tells you their pronouns, you have probably already used the old ones thousands of times — in your head, out loud, in texts to other people, in the stories you tell about your own life that happen to feature them. That repetition built a fast, low-effort retrieval path: you think of the person, the old word is just there, arriving before the sentence has finished forming. Believing something new does not erase a path that well-worn. It adds a second, newer path next to it, and for a while the old one is still faster simply because it has had more practice. A slip is that old path winning a race it has run ten thousand times before against one that has run ten. It is not a referendum on how much you care.
Practice away from them, not on them
The instinct is to be extra careful in front of the friend, which sounds right but usually backfires, because the first several attempts at a new retrieval path are the clumsiest ones, and doing your clumsiest reps in front of the person you're trying to get right for adds a layer of performance anxiety that makes slips more likely, not less. It works better the other way around: rehearse away from them. Tell a mutual friend a story about them and deliberately use the new pronoun. Correct yourself out loud when you're alone and catch an old habit forming a sentence. Reread a text thread with them and narrate it back to yourself in your head with the right words. None of this requires their patience, and it means that by the time you're actually talking to them, you've already run the new path more than a handful of times instead of starting cold.
Attach it to something you already remember well
A pronoun sitting by itself in your memory, disconnected from anything else, is unusually easy to lose the retrieval race, because there is nothing pulling it up except the bare fact of trying to remember it. It works better tied to something you already recall without effort — the trip they just took, the job they started, the partner's name you never mix up. Whenever one of those easy memories comes to mind, let it drag the pronoun along with it on purpose, a few times, until the two are linked. You are not memorizing a fact in isolation; you are wiring it into a memory that already retrieves itself easily.
When you slip anyway
You will, at least a few times, especially in the first months. What helps is a short, calm correction — restate the sentence with the right word and keep talking — rather than a long apology that stops the conversation and quietly puts your friend in the position of having to comfort you about your own mistake. A big, drawn-out apology can end up centering your discomfort instead of their experience, which is the opposite of what it's trying to do. A quick correction says the same thing with none of the extra weight: you noticed, you fixed it, it's not a big deal because it genuinely isn't one.
It is slower with people you see rarely
All of this is harder with a friend you only see once or twice a year, because you get almost no reps between visits, and each time you see them you are starting closer to cold than you were the last time. If you keep any kind of note about people you don't see often — even just a line to yourself before a visit, reminding you what's changed since you last talked — that is exactly the kind of detail worth putting in it, next to the other things you'd want to remember rather than have to ask about again.
The honest caveat
None of this makes the process instant, and it is fair to be a little unimpressed with yourself if it takes months rather than days — that timeline is normal, not evidence that you don't care as much as you think you do. What actually tells your friend how much this matters to you is not how fast you got it perfect. It's what you do in the seconds right after a slip, and whether you're visibly still working on it three months in rather than having quietly stopped trying.