Whichever of my many readers has tried to seriously write or actually does write fiction probably gagged a little bit upon reading that title.

Right, guys? I… mom, are you on your phone? Seriously? You are the only person in here AT LEAST PRETEND TO BE HAPPY FOR ME
Anyone that says that you should just write what you know should be electrocuted, but then again, I’ve never been electrocuted, so WHAT IF THAT’S JUST TOO MUCH!?
Still, there is something to be said for taking inspiration or knowledge from what you actually do know. You really can’t just suddenly write about shooting fireballs, because the big difference between Fan Fiction and an actual piece of writing is that it makes some sort of internal sense that at least reflects some basic understanding of external, real life sense. For example, I can forgive you for completely hand-waving anti-gravity on a starship by going centrifugblahblahblah, but you’d better pay attention to the limitations of that plasma gun, because if it starts out very specifically firing bolts of hot death and then you suddenly use it as a plasma cutter without referring to its ability to be adjusted beforehand you are not tricking me.
So, there is something to be said for knowing things at least a bit before writing about them. For my latest story, which you people have so unhelpfully not given me a title for, I looked at population density maps of Texas to determine where a landmark-less town that bordered on absolute nothing and that no one cared about might be located at some abstract point in the future (the answer was Temple, Texas), primarily so I could just make things up as I went along. You can still write fantastic, out there stuff, it just has to have some loose relation to human knowledge. For reference, purposefully ridiculous or abstract things don’t count here. That’s what makes them ridiculous or abstract.
The most difficult part of writing about things you have not experienced is when you have to write characters. Now, making a Wood Elf might be easy because no one has met one. You can justify almost anything in a universe you entirely created. But making, say, a human character of the opposite gender? If you blow it, you end up like Stephanie Meyers and write a rapey-sparkle-fairy because you accidentally the whole Y chromosome. Good enough for the pre-teen girl market, not so good for being remembered and keeping your books out of landfills. Funny thing: it’s useful to actually meet someone of the opposite gender before writing about them - I’m LOOKIN’ AT YOU, BRONTE SISTERS.
Yeah, I’m pickin’ on the lady authors. Deal with it.

Remember: A model does not count as an actual member of their gender or species, nor are they protected by the Geneva convention, being non-human.
Seriously, read up on how our brains work differently or something, but whatever you do, don’t just wing it. Strong female characters are not women that can play football just as well as the boys, and, like, totally take out the linebacker, and, like, put him in his place and stuff without messing up her eyeliner. Men are not allowed to compete against Women in Olympic sports (Curling does not count) because the Men would destroy the Women, unless it’s gymnastics, in which case flip that around. That’s just down to physiological differences.
When it comes down to it, Women don’t really do football, bro. I mean, yes, Samus Aran can take you out, but at the end of the day when all the Space Pirates and Metroids and all that bull is over, I’m sure she likes occasionally lookin’ pretty, and shopping sometimes. Ain’t nothin’ wrong with that. As a side note, Samus is basically a sex object, so don’t read too much into that example.
Gender inclinations are not some invention of The Man that exists purely to keep you down, so chill. I know you may be in your college years, when you might forget how to gender and decide that the past several thousand years of human development are wholly and irrevocably backwards, but you’ll figure it out and remember you’re not bi eventually. The point here is that these things become a problem only when either you ignore them, or you stress gender inclinations to the point at which it’s insulting and two-dimensional.
Sure, it’s valid to do a more macho female character, but seriously, we all know Vasquez was a lesbian, despite her attachment to… that other guy with the smart-gun. He didn’t last ten minutes, so I don’t remember his name. Anyway, I never believed that was more than a gun-buddy (pun unintended) relationship for a second. Maybe that’s terrible of me, but seriously.
Ripley on the other hand is quite clearly feminine (the smallest underwear of all tiiime), but still went all “lemme strap a flamethrower to this gun and kill everything” at the end of Aliens. You see, it was because she had lost her daughter during her fifty years of cryo-sleep, had encountered an orphaned young girl, and had some mama-trauma(tm) to work out, which she resolved by not letting said orphaned young girl get chest-bursted. I am fully aware that her name is Newt, so don’t even start with me. In fact, her given name is Rebecca, so double don’t start with me.
Even then, Ripley didn’t whip out some magic judo. She had a bazillion weapons strapped to her, and got the basic drill on how the weapons worked from Hicks earlier in the movie. Acid blood or no, you do not attack a really ticked off person with a flamethrower while she’s standing over your eggs. They were the Alien Queen’s babies, and you aren’t gonna be the first guy to leap off the wall, because if you get an egg torched, big mama’s gonna bite your head off. Literally. Ripley survived that whole encounter because she had a card to play (a belt of grenades and fire) and enough angry to pull it off. There ya go, blue collar spacer lady does something awesome.
None of this makes that whole last bit of Aliens any less hardcore. In fact, it makes it more hardcore. Ripley ran in there thinking “I have no idea what I’m doing, but by God I will hug you and set off every one of these grenades if you do not give me that little girl back.” The final confrontation was her going “Alright, it’s on, now. I have a Class C license and this thing with absolutely no armor, but I’m ticked, so let’s go.” Again, no magic judo, it was brute force and throwing the powerloader on top of the queen into a pit. She wasn’t a Jedi, she was mad. Ripley’s strong because she won’t give up, not because she has any idea what she’s going to do when she doesn’t give up. She doesn’t have any inexplicable capabilities, it all makes some sort of real world sense.

I don’t know where I’m going to shove what, but something is getting shoved somewhere and YOU ARE NOT GOING TO LIKE IT
So that’s enough about the lady-characters.
Ladies, when you write a dude, we are both not complete morons, but will also not maintain a state of flower-buying forever. It’s not because we don’t love you, it’s because our concept of romance is different. If you have a bunch of guys in the friend zone and wonder where all the nice guys are, just think about that for a second. The lower, background part of your brain doesn’t want a nice guy, it wants a guy that can support a family, which in cave person terms equates to punching because your brain still thinks that Sabretooth Tigers are a thing. This is why you date douchebags. They chest-pound. Use the upper brain-bits please. I will cover why this matters later.
Guys, you can start paying attention again.
In a relationship, women, chemically-speaking, want safe babies and a roof, and men want emotional and sexual gratification. It’s not a two way street, it’s two separate one-way streets which are totally different, but the traffic has to even out between the two of them. The dude keeps the bills paid, and the lady occasionally takes off her clothes. Simplified? It’s called a generalization. Crass? Okay, possibly. Still basically true? Yep. That’s the basic biological model.
That said, I fully own up to Always with Richard Dreyfuss being a great movie, and Carnival of Rust by Poets of the Fall is the third most listened to song on my iTunes. You can know why a sunset looks the way it does and still think it’s rad cool, maaaan.
Now, you may wonder why I dove off into relationship advice. There are two reasons.
1. Demonstrating my understanding of relationship mechanics will obviously make me a more attractive mate.

Those goggles were filled with vodka. I’m so lonely
2. Because understanding how a successful relationship works is actually a HUGE DEAL when writing relationships between characters, or simply writing a character of the opposite gender to the author, because relationship mechanics encompass how the genders will act/react differently to things.
So, you can have a magnificently beautiful woman in your book who is impossibly graceful and wonderful and nice and smart and stuff - but she ain’t gonna jump up and dual-wield swords. I have a character in my latest story that is near-ethereal in her improbable grace, and she’s a surgeon, not a machine-gunner. So yeah, she sees blood and bodies, but is gonna flip out a little bit while the guns are going off. Different paradigms, there. If she were supposed to be a Field Medic, things would be entirely different.
Similarly, you can have a mega-buff dude who throws trucks to protect his woman, but if he watches her sleep and calls her his own personal heroin he is going to kill her, rape her, and wear her skin. IN. THAT. ORDER. The main character of my latest story is a PTSD Marine. He is therefore pretty good at killing people, but he has watched friends die of poison gas (it’s the future), and stabbing, and getting their faces blown off. He’s not going to think to buy a Hallmark card “just cuz”.
Seriously ladies, as a side note, if a dude is following you around at weird times he’s a stalker, and that never ends well. Call the police. Any man with a healthy mental state will speak to you on normal social grounds rather than follow you at all hours…
…Or he will just hover on the periphery of your social circle because he’s a wuss.
Then he will gradually become sad.
Then he will get crazy-straw glasses and fill them with vodka as he sits at home writing a blog entry for his mother to read and sobbing uncontrollably.
Where was I…?
Ah, um, please don’t make my eyes bleed by writing cruddy characters in a shoddy duct-tape world. Yeah.