Setting

To me, the setting is not a very important part of creative writing. However, there are a lot of people that really like to know exactly where the characters are at and when. I like for things to be open and timeless. If, though, you wish to create a setting, make sure you are completely aware of it.

Place:
If you have not been to the place you are writing about (which is the best way to write about a place) then you need to research the place extensively. Make yourself familiar with it completely. The place is weather, things to do, the people, the food, culture, etc. You need to know about all of that stuff.
Personally, when I do decide that I'm going to give some kind of setting, I tend to make up a fake town or city. It is much easier to deal with, so that I don't mess up with what is in the real town.

Time:
Time is a little more difficult. If you go into the past, there are a lot of things that you could easily mess up on. Such as, you might be too far back in time before there were even numbers on houses. Check technology advances of the time. Your editor will know some of these things better, but you have to have the credit of knowing the time.

Honestly, setting is mostly about researching so you get it right!