Don't make the ending too rushed. If you've built up a complex plot, take the time to wrap it up properly. A rushed ending might leave the reader feeling like they missed out on something important. For example, if a long - running love story ends with just a quick 'they got married' without any real build - up to that moment, it can be disappointing.
Never leave the ending completely open - ended without any indication of where the story is going, unless it's part of a very specific writing style. Most readers like to have some sort of resolution, even if it's a bit ambiguous. For example, a story that just stops without any conclusion about the main character's fate will likely leave the reader frustrated.