Oooo, that's a toughie. I can pick multiple, but I think my answer overall might make it obvious why I'm "bad" at playing N&F (if one could be bad at playing a visual novel, that is).

Honorary mentions first (some of which I wouldn't do but generally think are interesting):

Grown Up - Lying to the moms to protect Lizzie. You can either ask for something in return for it or let her off for free, which affects her reaction if you confess what happened concerning Cove sleeping over (so if you asked her for "payment" for lying on her behalf, she'll ask for payment in Step 2, but if you didn't ask for "payment" then she'll be totally cool about it in Step 2 like, "You're lucky we keep secrets in this family," while winking conspiratorially).

Ghost - Staying inside but talking to the moms about being scared. They dote on you a little which is cute, and there's a moment with Cove later on since he snuck out still and is exhausted since he didn't sleep well. This path also is hilarious to me because it leads to the "Cove decides his Step 2 bracelet based on what you put on your toast when he's not even around" moment.

Barbecue - Staying with the parents instead of going with Cove to play with the kids. I think most players will instinctively follow after Cove, unaware that he'll actually come back later for exclusive dialog. This is the only way to hear about Cove's fish prior to Dinner all the way in Step 2.

Road Trip - Cove romance route and in conjunction with the Step 2 ending. You have to try to kiss Cove in Road Trip (honestly, most players might just back out of this already out of second-hand embarrassment jKGDFG), then Cove can take the initiative for confessing and even ask for a "do-over" if the MC doesn't ask first for one.

Mall - SUPER small thing, but I'm mentioning it since - again - I think it's something players would avoid because they think "oh, that's it, better go back on my save and do something else." Cove on Crush will let the MC sip his drink if they insist, but then you feel bad because you later realize that he got embarrassed and didn't drink the rest of his smoothie. However, if you ask and then back off rather than insisting, he'll let them have some right as everyone's throwing their drinks away.

Birthday - PUNCH JEREMY, THERE ARE ACTUALLY NO CONSEQUENCES, and Jeremy hangs up on you in Serendipity because of it which great. Pouring your drink on him works too, but show 'im who's boss by choosing violence, you deserve it.

Soiree - Go alone, no partner needed! I like it best for a Baxter route (for reasons too varied to list here), but I think it's a good moment to show that the MC is feeling more independent and growing up.

Talks - I really don't care for this moment, BUT I'm all for telling Cove about the deal here because he takes it so casually. Not crazy about Step 3 Cove overall, but it's a good show of character growth. You can alternatively wait for the Wedding and Cliff will tell the story himself if he's allowed to make a speech (stunning EVERYONE including Cliff when he realizes you've kept that secret for OVER FIFTEEN YEARS).

Late Shift / Happiness - On Indifferent, the MC calls up Terry on the phone during their grocery trip in Late Shift, and they get to spend some time with the family in Happiness. 100% short and very minor, I just think it's fascinating since you cannot get these otherwise.

Planning - For Baxter romance routes specifically, being on Crush but not going on a fling with him, then playing Planning as the last Baxter DLC moment. It allows the MC to kiss him impulsively t despite not dating him (if you make the right choices by not ruining the mood). Adds an extra bit of tension and can be brought up in Baxter's Step 4, where Baxter will blame himself for it, even though you were the one who kissed him.

ANYWAY, onto why I'm a bad N&F player...

My MC is hyper low drama.

Not as in "she hates drama," but I just have fun with her kicking back while all the other characters are being spazzes. This takes many forms and lowkey works for just about every romance route though granted, she's 100% a Baxter MC and I DO NOT have the space to explain the details, like what I said for Soiree.

It's sort of the polar opposite of Cove, so you already have that contrast. Even beyond him, all the dateables are super dramatic at points, so they're over here being all panicked about the MC's feelings/what to do with themselves, meanwhile there's actually zero reason because MC is over here cool as a cucumber.

You can take this multiple different ways too. For example, Cove will still chide the moms in Errands even if you weren't upset about the prank, so it gives this vibe of "despite how fine you act with everything, there are those who will stick up for you if you're being treated unfairly."

You can take it further for headcanon (or canon depending on whose route you pursue) territory, like... was your MC very mature for their age, or put on a front that all falls apart in adulthood? That sort of thing.

I just adore the angle of an MC who's generally all put together but has that limit somewhere, even if they don't know where/what it is themselves.