I do a lot of sport, am president of a club, like spending time relaxing on my own, sleep a lot and also like to have a bit of a social life (by which I mean going out like once per week, which I realise is a lot less than some people. But hey, I'm paying £9k/year for this and I don't even like going out that much). I'm currently on track for a strong first in what my tutor says is "the hardest subject" (it's probably not actually the hardest - whatever that means - but it seems fairly intense to me and the material is tough), but all it takes is a big slip up at some point and poof.
I have a whiteboard in my room that always has a to-do list on it, and sometimes I'll get to the point where I'm crossing multiple things off the list not because I've done then but because I've just had to accept that I'm not going to be able to find time to do them. Organisation is key, but I think not being a perfectionist helps in that it means I am able to say "okay I've got 48 hours to do two pieces of coursework and four assignments, the assignments aren't assessed so perhaps I'd better just look over them rather than actually try and complete them all".
I'm by no means at the toughest or best uni for my subject though, and I imagine I could have it a lot worse. But whenever someone says something like "it comes naturally to you" or "you must be really talented at x" or "I have to work really hard to do y", my usual response is to want to tell them to **** off. Looking at some of the literature, the effect of natural/genetic talent on success really pales in comparison to the effect of hard work and practice; people need to stop bitching that they're "just not good at a, b or c" and start working harder at a, b and c.
Anyway, my advice to people would just be to really start organising yourself. Get a calendar and start using to-do lists. Depending on your social life, workload etc. it may not magically boost you straight up to a first, but I'm pretty sure it will increase your productivity and academic achievement to some degree.