I am looking for a saying or common expression to say that it is not advisable to anticipate or celebrate something before you know the actual outcome. I am thinking about political elections or football match results, but also more everyday expectations about a possible positive outcome.
Don't sell the skin before you've caught the bear.
Never sell the bear's skin before one has killed the beast.
The die hasn't been cast (yet).
The final/last word hasn't been said/spoken.
It hasn't all been said yet.
It ain't (all) over (and done) yet.
One must not be too hasty in one's rejoicing.
I think this is a useful saying that may fit what you are looking for
Don't count your chickens (before they're hatched)
something that you say in order to warn someone to wait until a good thing they are expecting has really happened before they make any plans about it: You might be able to get a loan from the bank, but don't count your chickens.
"It isn't over till the fat lady sings".
Also, "It isn't over till it's over". (Politicians and journalists in Britain and America alike trot out this platitude all the time when elections are on.)
"Don't speak too soon" - could also work here.
speak too soon
Assume something prematurely, as in I guess I spoke too soon about moving to Boston; I didn't get the job after all .
And then there's the Yogi-ism, It ain't over till it's over.
Yogi-isms are the sayings of Yogi Berra,a famous baseball player and manager. http://en.wikipedia.org/wiki/Yogi_Berra
In addition to the other good answers, there's also:
It's more common to say:
Don't celebrate too soon
than to use early.
I think most of these other possible answers are either a bit too general, or off target in terms of celebration. I prefer:
Keep the champagne on ice
It implies there will be celebrating in the near and foreseeable future, but not immediately, so we will continue to keep the bubbly on ice.
However, it could also be used ironically or derisively, to burst another's bubble if they seem to be a bit too optimistic.