If you have an enemy who escapes justice somehow, make sure they learn from their previous mistakes. The heroes shouldn't be able to defeat the bad guy the same time again, and the villain shouldn't fall to the same vulnerabilities or lapses of attention.
Well, unless they're your typical James Bond villain, in which case they should be exactly as stupid as the first time. Only with a bigger volcanic lair and more piranhas.
C-3PO: So Artoo, what happened when you plugged into that door?
R2-D2: It was Nute Gunray. He was ready for my anti-viral system this time, and he overloaded the port so it wouldn't take him down.
[SFX]: < ooyoo-bippity doing-cheep bip dip-deep poppy-cheep spip-poppy boop poppity >
Chewbacca: The Nutes are learning... Each time we face him it's going to get harder.
C-3PO: Nute! I forgot to pretend to be him in front of the Ewocs!
Unidentified Ewoc: It doesn't matter, you were acting in your own self-interest. So Nute was truly inside you the whole time.
C-3PO: Oh my. Um... thanks?
Lando: So, Chewie, wanna ditch your freshly hitched friend and be my co-pilot? You know your way around the Falcon.
Chewbacca: I've had worse offers.
Han: No, you're sticking with me!
Leia: On our honeymoon?
Chewbacca: Lando, when do we leave?