While I'm not saying that every successful person's life is the same (far from it), I am saying that the majority of them follow at least a few of these key principles that I'll outline, and that the more of them a person follow, the more successful they're likely to become.
The most important thing (above all) is to lead a balanced life.
This means not working so much that you don't have time for all of the other important things in life.
Sure, it's okay to indulge every once in a while and to go really into something, just as long as you always come back and readdress the balance.
One thing that most people don't realise is that leading a balanced life is something that you have to work on every single day.
You might think that you can get the balance of work, socialising, exercising, relationships, etc.
right and then never have to worry about it again, but it simply doesn't work like that! The best way (that I've found) to making sure that I don't work too long is to set working hours in the day (such as 9-5) and not working outside of them.
Obviously this requires a lot of willpower and persistence, but the results are definitely worth the effort.
Note that there's nothing wrong with doing lots of work, but there is something wrong with working for too long.
Interestingly, I've found that if I know I've only got 5 hours to work in (and 8 hours of work to do), I'll focus more and work more efficiently.