Lots of good advice from Chuck. One thing, though: don't leave it too late. If you can retire well before the mandatory age then do it. This way you'll have plenty of energy and your life expectancy - in your own mind, and this is important - will be one where you're thinking you can do a lot in the years ahead. Generally, people who work right up until their employer gives them the proverbial 'gold watch' and wishes them many days of 'happy fishing.' tend not to last long.
As Chuck says, it's admissable to have an income that you feel you can live reasonably comfortably on. So when you get that final paycheck along with the super payout DONT go on a worldwide three month holiday and buy that brand new car...well, not unless you've got a real lot of money. The tempation will be there but don't do it.
Also, start thinking seriously about what you really want to do with your life. You will now have the time to do things you never had enough time to do before. But balance out your life between adequate exercise, adequate mental stimulation, and adequate spiritual pursuits. We are body, mind and spirit after all.
It sometimes takes a bit of courage to know when to retire. Old habits and indentifying with what we've been doing all our lives is not always easy to leave behind. But if you do it right, you will find - as I certainly have - that retirement can be the most productive and enjoyable years of your life.