We all have a wishlist of things we’d do if time travel were possible. It’s a common human fantasy: who wouldn’t want the ability to wander through history, and, if you’re exceptionally careful about it, even change it? But with great temporal power comes great temporal responsibility—and the huge potential for big mistakes. Paradox-level mistakes. Massive, existence-wiping mistakes. Over the years, science fiction and fantasy have provided something of a guide to the pitfalls and dangers associated with traveling through time. Here, for your edification, are 10 suggestions for what to definitely not do, should you happen upon a TARDIS on your way home from work.

1. Forget your history lessons

In Wesley Chu’s Time Siege, disgraced time agent Levin Javier-Oberon is sent to salvage supplies for the resistance effort throughout various time periods. All goes fairly well (in spite of Levin’s complaining) until he’s tasked with grabbing the goods from a military base amid a major battle. During the salvage, he’s forced into a split-second decision and forgets the historical chain of events, leading to a ripple effect that changes a significant moment in Martian history. It’s only later that he realizes the base he’d interfered with was an important landmark during the war between inner and outer planets (and seriously, why is it always the inner and outer planets?), with far-reaching implications. It’s a good idea to have a quick period refresher before traveling back. Who knows what you might cause otherwise?

2. Treat history like a petri dish

The late, great Kage Baker’s Company Novels are about a group of immortal cyborgs and uplifted hominids working for the shadowy Dr. Zeus, Inc. Dr. Zeus and the AI at its head operate by sending agents back in time to find artifacts and areas that serve Company interests, so the Company can later “discover” them and reap the benefits. Meddling with the forces of evolution and taking an active role in shaping history for its own ends comes back to bite the Company when it is ultimately the target of a multi-gambit pileup involving time clones, its own agents and executives, and a plague cult set to wipe out all (mortal) life on Earth. Worse still, the Company kind of engineered its own end by broadcasting the date when its timeline goes dark, allowing everyone to know exactly when to make their move. It might even have started the entire chain of events by wiping out a cult thought a hindrance to progress and civilization. The world, and indeed time itself, are not toys. Do not treat them as such.

3. Signal your presence

The protagonists of Replay, by Ken Grimwood, have an odd method of time travel. Upon death, their consciousness is sent back 25-odd years into their own bodies, with all future memories intact, to relive the same number of years time until they die again, at the exact same moment—creating a kind of Groundhog Day loop. Naturally, the first thing anyone does is fix old mistakes and use their foreknowledge to become fabulously wealthy, then begin mucking about with history. These actions reach their peak when one of the replayers decides to enlist George Lucas and Steven Spielberg to make her a science fiction film, with the specific intent of finding and meeting other people replaying their lives. It also turns out to be a horrible idea, since at least one of said travelers is a deranged murderer, and a shadowy government agency may be actively seeking replayers for their own nefarious purposes. Telling people when you’re from is usually a bad idea in general anyway.

4. Annoy other time travelers

In The First Fifteen Lives of Harry August, by Claire North, time travel also works in loops, with “kalachakras” being sent back to the start of their previous lives to live out events with all memories intact, unless someone interferes. When one kalachakra decided he wanted to play around and uplift a medieval court, he caused a ripple effect, brought about the end of the world via nuclear holocaust, and alerted a society of fellow kalachakras to his presence. In the interests of keeping things classy for my readers, I won’t go into detail, but when people have all the time in the world, a distinct grudge against one person, and they know when that person will appear in the timeline, the results are not pretty. Respect your fellow time travelers, people. Otherwise you may wake up and find out you have a history of trauma, and have also ceased to exist.

5. Fixate on future events

Jay Asher and Carolyn Mackler’s The Future of Us is the story of Josh and Emily, two mid-’90s teenagers who discover that they can access their future Facebook profiles, never mind that Facebook hasn’t been invented yet, the profiles describe events taking place 15 years in the future, and that accessing the site via a 2600 baud modem would be its own special hell. As they begin to check the pages more and more obsessively, they discover they can alter the trajectories of their futures based on small choices they make, and begin to try and alter their presents to game their futures. Fixating on the future at the expense of the here and now is generally a bad idea, but it can have disastrous implications when that info is all you rely on. Let some mystery remain. It’s better that way.

6. Plan too rigidly

The future humans of Millennium, by John Varley, do their best to account for everything. Their plan is fairly simple: they kidnap people who were going to die anyway, leave realistic synthetic bodies in their place, and spirit the survivors off to a population-ravaged future. They have a strict timetable, and they stick to it. Usually, anything that might give them away is destroyed in the crash. That is, until the passengers of one plane crash decide to fight back, and things go spectacularly wrong, leaving a bunch of burned up bodies with watches running backwards, a suspicious flight recorder, and, most damningly, a futuristic stun gun. The repeated attempts to recover the gun and reset the status quo lead to more and more ripples in time, and even more attempts to fix them. Murphy’s Law is a law for a reason, and doubly so when ripping the time/space continuum a new one.

7. Split yourself across timelines

In Steve Aylett’s pitch-black absurdist comedy Slaughtermatic, Dante Cubit thinks he has planned the perfect bank heist. Unfortunately, it goes horribly wrong when he realizes the blueprints he used were for another building. So he clones himself into the past to clear out the vault, rejoin his gang, and then die. Things go from bad to worse, however, when the time-clone refuses to die, and both of them start fading out of existence. If that weren’t complicated enough, Dante’s heist sets a murderer’s row of criminals on his trail, because while a paradox is bad, it’s even worse in a city where absolutely everyone is a maniac. When messing with time travel, simpler is always better.

8. Do experimental drugs

In The House on the Strand, Daphne du Maurier tells the story of a man named Dick who wishes to escape from the drudgery of his life with the aid of an experimental drug called Kilmarth. With the drug, he can go back and inhabit the early 14th century, and in particular, follow the lives of Roger and Isolde, two star-crossed lovers. But abusing pharmaceuticals with time traveling properties is about as dangerous as it sounds, as Roger’s addiction drives him to near-murder and debilitating physical illness in the present day. The drug’s maker even leaps in front of a train while on a Kilmarth trip. While a method of time travel is one of those things one should take as it comes to them, perhaps leave the drugs alone. Or have a really good spotter with a knowledge of medieval history…but not everyone knows a bunch of hip friends who were also in the SCA.

9. Contract rabies, crash a car to send yourself back in time, then try to murder your own ancestors to gain superpowers

There is no way to completely explain what in the name of all that is dear and fluffy was going through the title character’s head in Chuck Palahniuk’s Rant: An Oral Biography. Whatever it was, following the lead of a Chuck Palahniuk character is a great reason to seek therapy and a terrible reason to time-travel. No. Just…just no.

10. Panic and try to fix things

Connie Willis’s To Say Nothing of the Dog is best described as a four-dimensional comedy of errors. A team of researchers goes back in time to find a ceramic atrocity called the Bishop’s Bird Stump that’s supposed to sit in the restored Coventry Cathedral. Things begin to go wrong immediately, stranding one of them in the 19th Century with very little idea of how to carry out his mission. As the heroes attempt to recover the stump (whatever it is), their actions cause unusual ripples all over the timeline. Most everything would have been more or less fine had they not decided to scramble all over the place trying to fix things, causing greater temporal disasters with every mixup. It’s more useful to take a leaf from The Hitch-Hiker’s Guide to the Galaxy: Don’t panic.

What universe-destroying lessons are we forgetting?