(1) Give users the ability to mark posts as NSFW after making them. Right now, we can only mark posts as NSFW before posting them afaik.
(2) Limit the amount of space videos take up on the screen. I upload videos to catbox.moe and then post their links in the URL textbox. The problem is that right now, if you click on a video post, the video can fill up 2/3rds of the screen or even more, making the video clip unwatchable. To work around this issue, you can use the zoom out setting on your browser but that makes this more complicated than it should be. A fixed-size or proportional-size video playback frame (is that the right technical term?) is needed.
Both those things are heavily dependent on the front-end UI you use though. There are a ton of 3rd party desktop-web and mobile apps now that present and interact with lemmy in different ways and users will have many different experiences than yours.