That's a difficult question, I feel, because if a scene doesn't have a strong start and a sustained energy then it is much harder to end well.
But if all is working well and as it should be, then there are a few things you can look for:
1) A pattern or Game is hit three times.
2) A huge laugh line is delivered.
3) An emotional change or realization is made.
4) A shift in status occurs.
I personally prefer (3), but depending on your style of play you might do well with the other choices. In regards to (1): This is basic comedy structure we're talking about here; funny things just seem to come in threes. Naturally, we have to be sure that the funny thing, the pattern, the Game, is valid enough to warrant being used this way and it should be organic as well. No one wants to see a joke hammered three times into a scene just for the sake of making an ending possible.
The cool thing is that by identifying these 4 things, we can then just workshop hitting Game, or emotional changes, or status shifts and see which ones work best for us.