1) If Captain Kirk invites you on an away mission, don't wear your red uniform
2) It is not important to learn people's names, you just need to know what they do and add Mr or Ms to it (Mr Conductor, Mr Mailman, Ms Librarian, etc)
3) Dogs can talk and communicate with people, though most people do not seem to pay attention or have the ability to "hear" them. This may apply to other animals as well
4) If the only person who looks you in the eye and talks to you is psychic, you might be dead
5) If you hear creepy music in the background (especially if you are alone), your probably going to die soon
6) If you find yourself playing doctor in an emergency room, and an emergency comes in the door. Don't panic ! The solution to any problem is order a CT scan, chem7 and CBC, unless they have no insurance in which case you send them to another hospital hundreds of mile away.
7) Suspects, if brought into a small police room and when confronted with only circumstantial evidence under a bright light will almost always confess to the crime. (especially near the end of the show)
8) Corollary: If a suspect confesses to early in the show, he/she really didn't do it.
9) When time travelling to save the world, you will soon come to learn that saving the world would never had been necessary if you never time travelled in the first place.
10) All computers are connected together all the time, even when turned off. and any password on any computer anywhere (including secret FBI, CIA, etc) can be discovered within 3 password attempts
11) Don't order a TAXI when you go into labor, you will never make it to the hospital
12) If the "bad guy" catches you. No worries ! Instead of killing you on the spot, he/she will first reveal his entire plan fore world domination and then leave you alone in a room with some really complicated setup to kill you. This will give you will have plenty of time to escape and thwart his evil plans.
13) You know you are on the 'good side', if you can run away at point blank range whilst being shot at by dozens of other people, and not get hit once.
14) If you want to throw food at someone, you will always miss who you intended and hit someone else, the person throwing back will miss you ending up in a big food fight involving everyone within a 50ft radius
15) You never need to go to the bathroom, and if you do go into one, it will never turn out good.
Please feel free to add more in the comments, and pass it on !