It's summer, which means that the movie theater lobbies look oddly familiar because so many of the posters are for sequels of movies we've seen before (sometimes numerous times). But what sets apart a good sequel from a bad one? It's not simply a matter of getting the band back together, moving the action to "the Hood" (alt: Outer Space) and upping the body count; there are many tricks that have been played over the years that have elevated what might have been simple cash-grabs into legitimate works that stand on their own.

Here are a few of the tried-and-true tricks to making a solid sequel, as well as some of the films that pulled it off... and a few that didn't.

1. Introduce New Blood

One thing that all sequels need is some element of newness. After all, while people came to see the sequel because they loved the first movie, they don't just want to watch the first film over again. (Otherwise they would.) One of the simplest ways to do this is to bring in colorful new characters. (Note: There's no need to get too literal, like Friday the 13th VII: The New Blood. We'll get the picture.)

Nailed It: Shrek 2

Puss in Boots was the best thing to ever happen to the big green guy and his lady.

Failed It: The Hangover Part II

They literally have the same exact people doing the same exact things as the first film. Only it's in Thailand, get it?! No.

2. Switch Up the Genre

How about continuing the story using a different set of film conventions entirely? It's not easy, but when it works it can be wonderfully effective.

Nailed It: Aliens, Texas Chainsaw Massacre Part II

Aliens picked up where Alien's atmospheric haunted-house horror film left off, but this episode was a full-bore action movie. People went Newts for it! And Tobe Hooper followed up his bleak, extremely effective survival horror film Texas Chain Saw with... a comedy? Yes - it's one of the sickest comedies ever made, but it's also hilarious in all the wrong ways. Even the movie's poster was a WTF? parody of The Breakfast Club.

Failed It: Texas Chainsaw Massacre: The Beginning, Saw

This "origin story" of Texas Chainsaw was exactly the same as the remake of the first film, and could have benefitted from a little creativity. Only it co-starred Matt Bomer, so it had that going for it.

3. "Don't F*ck With the Original"

In the wildly meta Scream 4, Neve Campbell's beleaguered Sidney Prescott utters the priceless words above. And she's right: if people are coming back to see a sequel, chances are they really dug the original. Don't go getting all revisionist and actually rewriting the essential elements of the first film.

Nailed It: Scream 4

Scream 4 managed to honor the original film and characters while telling an entirely new chapter of the story, all with the series' trademark self-awareness.

Failed It: The Matrix: Reloaded and Revolutions

Remember that awesome feeling at the end of The Matrix when Neo was the chosen one and he could slow down bullets and shit? Well, forget all that - they got a little ahead of themselves, and spent the next twenty hours undoing their brilliant first act.

4. Up the Stakes

If the first movie's about saving a cheerleader, the second movie better be about saving the Dallas Cowgirls.

Nailed It: Airplane 2: The Sequel

What's worse than a plane without a pilot? A SPACE SHUTTLE without a pilot! This guy would agree. As would Pat Sajak, above.

Failed It: Ocean's Twelve, Ocean's Thirteen

By the third Ocean's film, they would have had to have been robbing the World Bank in order to fund a bone marrow transplant for Scott Caan to make it worthwhile. But no, it was just more of the same.

5. Flesh Out the Mythology

Nailed It: X2: X-Men United, Star Wars Episode V: The Empire Strikes Back

Empire transformed the Star Wars franchise from a fairly simple sci-fi swashbuckler into a sprawling, dense space opera. Likewise, X2: X-Men United built out the individual stories of the core mutants while making the story infinitely more grand.

Failed It: Exorcist II: The Heretic, Exorcist: The Beginning

It's amazing that one of the greatest horror movies of all time has two of the lousiest sequels (and I'm not even going near the godawful Dominion: Prequel to the Exorcist). Instead of building context around the story of Regan's possession, they simply confused it. On a positive note, The Heretic does feature one of the greatest tapdancing numbers in horror film history.

6. Mix Up the Formula

The third film in a series is usually the hardest to land, and the point where people start to get desperate (Hello, Jaws 3-D!). So instead of resorting to a 3-D gimmick, these two healthy franchises decided to tweak their formulas. One worked, one didn't.

Nailed It: National Lampoon's Christmas Vacation

Guys, this is a Vacation movie where the Griswolds don't go anywhere. And somehow it totally worked - we actually learned more about the central family, and of course Christmas movies are just awesome in general.

Failed It: Halloween III: Season of the Witch

Okay, we get it that you were tired of being a slasher franchise. But take away the slasher franchise and what is Halloween? Apparently it's an extended Goosebumps episode about masks that make spiders come out of kids' mouths. NOT COOL. Sure, the film's kind of a hoot on its own, but it's as much a Halloween movie as those godawful Rob Zombie remakes.

7. Let It Grow Up

So your franchise is aging, and so are its characters (and, perhaps even more importantly, its target audience). And there's nothing wrong with that. Let the flavors ripen along with your talent! Many a poignant second act has come from adolescent beginnings.

Nailed It: Harry Potter and the Prisoner of Azkaban, Before Sunset, Toy Story 2.

Failed It: Batman & Robin

No, "growing up" does not mean "nipples on batsuits".

And, if all else fails...

8. Get Bruce!

When you run out of ideas, simply add Bruce Willis. For one, he's been in more sequels to his own movies than you can shake Cybill Shepherd at (Die Hard 27: Die Mommy Die Hard, The Expendables 2, The Whole Ten Yards - yes, that really is a thing). Heck - he's such good sequel karma that they even add him to sequels of movies that he wasn't even in to begin with.

Nailed It: Die Hard 2, Die Hard With a Vengeance, Charlie's Angels: Full Throttle, G.I. Joe: Retaliation, Ocean's Twelve

And just for fun, here are some more sequels that we think nailed it and failed it.

Nailed It: 28 Weeks Later, Back to the Future III, The Dark Knight, The Empire Strikes Back, Spider-Man II, Terminator 2: Judgment Day, Toy Story 2, The Godfather Part II, Star Trek II: The Wrath of Khan, Superman II, Lord of the Rings: The Return of the King

Failed It: Return to Oz, Indiana Jones and the Temple of Doom, , Jaws 3-D, Jewel of the Nile, Teen Wolf Too, The Godfather Part III, Star Wars: Episodes 1-3, Batman & Robin, Caddyshack II, Staying Alive, Exorcist: The Beginning, I Still Know What You Did Last Summer, Grease 2, Ghostbusters II, Highlander II