1. Never directly explain the action. People read partly for the pleasure of figuring things out for themselves. Don't deny them that pleasure. Which is to say, avoid things like Jimmy picked up the bundle and stormed away because he was angry. We can figure out that Jimmy was angry, really we can. If you write a sentence using the word "because," you might be well advised to just delete it.
2. Never sum up. Readers are bright. See above comment, but mostly I mean don't sum up the story for the reader at the ending. Don't tell your reader the meaning of your story. The "meaning" of the story might be different for the reader than it is for you. It's also highly likely that you don't know what your story actually "means" in a deep thematic sense while you're writing it (unless you are deliberately writing didactic or moralistic fiction, in which case your story
3. Leave them wanting more. Go out on a high note. Don't drag the ending out. Have you finished the necessary action of the story? Then get the hell out of it. You can get to the moment of crisis, assure the reader what's going to happen next, and then stop without even showing the crisis resolving itself. That's a cool trick.
Also! I am not even here today! Through the magic of the internets, I wrote this post last week or so, and this lovely Friday morning I'm on vacation! I will not be looking at this blog until, say, next Tuesday, so have a good weekend in my absence, and I look to Domey and Michelle to keep the commentary cracking with humor. So get cracking.