If you're going to go to the bother of planning a trap for the heroes, you have to make absolutely sure they fall into it. Some options:

• Put a big red button with the label "Do not push" on it. When (not "if") they push it, it activates the trap.
• Schrödinger's trap: Whichever way the heroes try to gain entry to the villain's lair, the trap is there.
• Make the trap have two parts. When they disarm the first part, the second part activates.
• Describe in detail something that looks completely harmless. Stress how innocuous it looks. Provide so many details of its appearance/sound/smell that the PCs will conclude it's important. If they test/scry it for traps, they find none. Don't even roll dice. Repeat over and over again that it seems utterly harmless. When they get so suspicious that they leave without touching it, exiting the room without taking the object triggers the trap.
• Have an obvious trap somewhere. Make it so obvious that as soon as the PCs see it, you just say, "You see an obvious trap". When they go near it anyway, it triggers.

Transcript

GM: You've landed on Koozebane. It's a desolate rocky world with a red sky.
Luke: Right. We need to find this Vader-clone, or whoever it is, and rescue Chewbacca.
R2-D2: The Force guided you to land right near him, right? Like when we found Yoda on Dagobah?
Luke: Uh, of course it already did that. Without me needing to say.
Gonzo: No, it was I! I guided you into the trap into which you have fallen!
GM: Corey, take this note.
R2-D2: You had to guide us into your trap? Not a very good trap then, was it?
Gonzo: Even so! Good enough to fool you! You fool!
C-3PO: You're the Sith Lord who kidnapped Chewbacca? I was expecting someone a bit...
Gonzo: Taller?
C-3PO: No. More evil.