One thing I think that would be handy is a client that lets you sign in with your own nsec, and then also someone else's npub, and makes it easier to just follow someone from that person's stream without the acrobatics of either signing back in, or juggling multiple windows. It's not THAT bad as is but you sort of have to know that it's what you want to do at this point, and I think new folks already have a hard enough time with the idea of being able to sign in as someone else in the first place.
Groups are another discovery mechanism for finding people to follow that just don't seem like they've ever caught on. Not sure if that's a UI thing or what, but they could be an interesting path if a spark lands on the right tinder.