#1. Human beings, despite being dumber, weaker, softer, and less technologically advanced than most alien races they encounter, someone always manage to outperform the more advanced races and Save The Day. Because, y'know, we're just so darn special.
#2. Any hideous bodily deformation (rapid aging, devolving into a lizard, etc), can be perfectly reversed.
#3. The twin is always evil.
#4. You can tell when you're time-travelling by watching the clocks.
#5. Significant urban renovation is strictly forbidden wherever someone is time-traveling into the future. Moving mannequins requires a special permit.
#6. The bigger the unstoppable doomsday machine, the easier it is to hit its weak spot.
#7. Despite the infinite vastness of space, every spacefaring race has nonetheless agreed on which way is "up".
#8. Genetic clones posesses all the knowledge of their originals.
#9. In the event of enemy attack, ship's system will fail in the following order: weapons control, helm control, shields, life support, communications, coffee maker.
#10. Godlike super-intelligent beings will have the emotional maturity of a 12-year-old.
#11. Automatic doors can tell if an approaching lifeform is going to walk through them, or just past them.