Names are all-important. Never use ordinary, common names like "Lisa" and "Brandon". All of your characters must be named something exotic that describes who they are perfectly. Trust me, no one will notice that you're using almost-forgotten Gaelic names in a place such as far-western Russia and that there is no way that the parents will have predicted that their kid will be the savior of the world at age fifteen.
Feet shall never be mentioned beyond how smooth and beautiful so-and-so's are. And, no matter how many times they wear their shoes, their footwear and feet will smell like a lovely garden.
If your main character is female, she must be spunky, rebellious, and very lively. She should preferably hate men, too, on the basis that "they're all chauvinistic pigs".
If your main character is male, he must be dark, tall, and brooding about his past mistakes, no matter how insignificant they are. He should also wear lots of black and/or blue and be able to wield a sword or gun three times his size.
Every story needs an evil genius, no "if"s, "and"s, or "but"s about it. He should also make lots of weird, high-tech stuff all the time.
Time travel is actually quite simple and easy to explain. You just don't have time to, that's all.
If you ever encounter an illogical moment in your story, or any odd moment really, you should say that you know it's not supposed to happen, but you're going to make it happen anyhow. Bonus points if you put it in parentheses.