I'm definately with the others! Check out Covent Garden. It's clean, it's safe and not so many youngsters as the restaurants tend to be a bit pricier. Leicester Square is also fun, but it depends how old you are. I am in my 40's and found there a few too many 20 somethings!
I quite like Soho also. Lots of lovely restaurants and great pubs. You can pop your head in and see what it's like before settling down for a meal or a drink also. Soho is pretty big so make sure you walk right round, as it's commonly thought of as the gay part of town but there are plenty of straight bars and pubs and great restaurants down those streets also.
And it's a short walk to/from Covent Garden.