You're thinking But, wait a minute. Stories are fiction. They're supposed to be made-up. They're not supposed to be true. This is a good point. But...
Know facts! Use facts! If your story is set basically on our Earth in basically our society with basic humans, you need to get basic physics correct. You need to know what gravity and electromagnetism are and basically how they work. You need to know about the sun and the moon and other planets and stars. You need to know approximately where the continents and countries and basic landmarks are. If you get any of this wrong with no explanation or confirmation my peeve will be activated. By confirmation, I mean more than one character or situation is involved in this difference from our world; somehow indicate this difference is intentional.
An aside on explanations: Don't over-explain. A pitfall of alternate history can be a lot of exposition about what exactly is different in history and what the ramifications were, etc. etc. In this case, don't explain, show.
Of course, all bets are off if your story is set on another world with other creatures, or if there's magic or other extenuating circumstances (unreliable narrator?) involved.
The submission deadline for the November 2016 issue is October 15, 2016! Send those stories in!