1. Give them makeovers.

As the educational film Earth Girls Are Easy makes clear, the easiest way to get an alien to go on an Earth-bound date is to offer him a makeover first. No alien wants to feel like he doesn't fit in at the disco, so have your cute friend (ideally, as cute as Julie Brown) give them a nice depilation treatment and wardrobe upgrade. Then you're ready for a night on the town. And if the ending of this movie is any indication, you'll have your de-furred, long-tongued alien purring in bed with you before the night is through.

2. Tell your alien a sob story about your last boyfriend.

This is really an advanced technique in alien seduction, but it seemed to work wonders for Karen Allen in the movie Starman. A friendly alien has come to Earth and used genetic material from her dead husband to craft a body for himself (that's why she didn't need to offer him a makeover).

When alien hottie asks her to "define love," Karen gives him the whole "when someone you love dies [sob]" number and it totally works! Later on, she takes a tumble with the alien out in nature — and that was back in the day when Jeff Bridges had a really hot body, so score one for Karen.

3. Have a warm body.

Sometimes you don't need a fancy makeover or tale of woe to get an alien babe's attention. The hot alien in Species just wants a warm body, and all you need to do is stand next to her when she strips off her top and shows off her bra. So if you're looking for a Species-style hookup, always remember to hang out in giant nightclubs that are near highly-classified research facilities. Just remember, if she decides not to have sex with you after assessing your genetic material, don't insist on it.

4. Make your alien feel like she owes you something.

Don't let anyone tell you that guilt isn't a good way to get some hot alien action. Look what happens in videogame Mass Effect when you put the old "you owe me something" attitude on. What I'm saying is that if an alien babe wants to thank you, always ask for more. Don't be satisfied with just a few wise words about your leadership or whatever crap. Keep pushing for the old you-know-what.

5. Join a secret organization whose job is to guard an ambiguous "rift" between Earth and vaguely-defined alien stuff.

This is one of those pickup artist tips that almost goes without saying. Obviously the very first thing you should do if you want to meet hot aliens is join a secret organization like Torchwood, from the eponymous TV series that spun off from Doctor Who. In this clip you can see the kinds of things that aliens do with our intrepid agents. The fact is, most aliens are on Earth looking for orgasmic energy and you just have to be in the right place at the right time to give it to them. But if that's too hard for you, well then obviously you'll want to go back to the makeover and sob story options. Or guilt. Aliens just love guilt.

WARNING: Do not, under any circumstances, expect your alien to act like this or like this.

What Women Want. Mel Gibson is an immature ad exec who doesn't understand female consumers and is mean to rising exec Helen Hunt. Until one day, he learns to understand the women's point of view.
Scifi element: Gibson gets struck by lightning while wearing pantyhose, and gains selective telepathy: he can "hear" women's thoughts, but not men's. It's not ever really explained what happened.
Creepy subtext: Gibson steals Hunt's ideas, undermines her, and uses his new awareness of women's feelings to become the ultimate slick marketing weenie.
How bad is it? It's hideously painful and awful. The part where Mel Gibson narrates a Nike ad and everyone swoons made me queasy. Here's the trailer:

Shallow Hal. Jack Black is an immature lout who only values women based on their appearance, until a self-help guru puts a whammy on him to make him see women's inner beauty.
Scifi element: It's really not clear. "Life coach" Tony Robbins has some kind of telepathic abilities in this movie, and he's able to restructure Jack Black's brain significantly. It could just be hypnosis, but seems to go a lot further, since afterwards Hal can see people's "inner beauty." It's almost as if Tony Robbins is a telepath who imbues Jack Black with a mild form of telepathy of his own.
Creepy subtext: Well, Gwyneth Paltrow in a fat suit is sort of hard to take. But also she just "happens" to be the boss' daughter, which makes Hal's attraction to her awfully convenient.
How bad is it? It's pretty terrible, what with the fatsuitage and the whole "Tony Robbins has mental powers" stuff. It's the only unbearable Jack Black movie.

I.Q. Tim Robbins is an immature garage mechanic who falls for Meg Ryan... who's the niece of Albert Einstein (Walter Matthau). Even though Meg is engaged to Stephen Fry from Wooster & Jeeves, Einstein decides to get Tim Robbins together with his niece. This involves lots of Einstein riding on Robbins' motorcycle and screaming "wahooo!"
Scifi element: Well, Einstein's plan to help Robbins and Ryan get together involves inventing a fusion-powered nuclear spaceship and giving Robbins the credit for it. That way, Ryan will realize Robbins really has a good heart. Which makes total sense!
Creepy subtext: It's yet another movie about Meg Ryan being engaged to a smart guy, when you know she should really be with the dumb guy instead. That's, like, Meg Ryan's whole career.
How bad is it? I saw it in the theater (why?!) and had managed to repress it totally until just now. One whole side of my body is now having shooting pains reliving the trauma of watching this movie.

My Super Ex-Girlfriend. Luke Wilson is an immature guy who starts dating Uma Thurman, not realizing she's a superhero and a psycho. He really likes Anna Faris, and when he hooks up with her, Uma goes nutso on him.
Scifi element: Uma Thurman is a superhero, who gets her powers from a chunk of meteorite. And a supervillain played by Eddie Izzard somehow knows that the same meteorite can take away her powers as well.
Creepy subtext: Luke helps Izzard to remove Uma's superpowers, even though this will allow Izzard to take over the world and stuff. Because there's nothing more important than getting your ex off your back.
How bad is it? It has a Rotten Tomatoes score of like -1,000.

My Stepmother Is An Alien. Dan Akroyd is an immature scientist who falls in love with a woman and marries her in like two hours, not realizing Kim Basinger is really from another planet! But she may have to leave him and go back to her planet. Can true love triumph? And what about Alyson Hannigan and Seth Green? Will those kids ever get together?
Scifi element: Akroyd somehow zaps another galaxy with his super space telescope. Don't ask me how. And Basinger's mission is to get him to zap her galaxy again, before some ill-explained disaster happens.
Creepy subtext: In her quest to be the perfect wife, Basinger learns about sex from her purse, and then cooks a few dozen dinners at once for Akroyd and his daughter, Hannigan.
How bad is it? It's definitely one of the lower rungs on Akroyd's climbdown into the scary dark place of his career. Not quite Blues Brothers 2000, but close. Here's a clip:

Earth Girls Are Easy. A spaceship crashes in Geena Davis' swimming pool, and out come Jim Carrey, Jeff Goldblum and Damon Wayans. An entire movie based on a comedy song by Julie Brown.
Scifi element: Carrey, Goldblum and Wayans are furry aliens, who turn out to be shockingly handsome once you shave off all their fur.
Creepy subtext: Davis' character is sort of a loser until Jeff Goldblum swoops into her life.
How bad is it? It's pretty cheesy, but it's pretty much just an MTV-esque musical.

Virtual Sexuality. Justine is tired of being a virgin, so she goes to a virtual-reality salon... only to bring her ideal man into existence in the real world.
Scifi element: Justine enters the "Narcissus machine" at the VR salon, which is supposed to reshape your face and body into your ideal appearance, but she decides to create her ideal man instead. But there's a gas explosion while she's in there, and her fantasy of the ideal man comes to life. (As a hologram?) The inventors of the Narcissus machine want to capture this embodiment of women's fantasies, but he's too busy being a studmuffin.
Creepy subtext: Because the "ideal man" is created from Justine's fantasies, when he comes to life he's freaky and effeminate.
How bad is it? It has an average critic score of D. But it's sort of charming, judging from this fan music video:

Mork And Mindy Famous TV show about Robin Williams' alien who comes to Earth and falls in love with Pam Dawber, along with everyone at home. How long before this becomes a hideous movie starring Will Ferrell?
Scifi element: Mork is an alien. He can drink with his finger. After Mork and Mindy get married, they have a kid... who's born as an old guy, Andrew Sean Greer-style, and then ages backwards.
Creepy subtext: Well, Robin Williams' whole cute innocent man-boy schtick gets a little weird.
How bad is it? Parts of it are great, but it went downhill fast.

Groundhog Day. Bill Murray is an immature wretch of a weatherman who finds himself living through the same day over and over. I wouldn't have considered this a romcom, but it appears on several lists of the genre. He does fall in love and end up with Andie MacDowell.
Scifi element: Time travel, although it's never explained and may actually involve magic or karma or whatever.
Creepy subtext: Well, Murray tries to kill himself several times, and acts like a total asswipe to people once he realizes everything will be undone at the end of the day.
How bad is it? It's actually pretty great. Either this is the exception, or it's just not a romcom.