First, ask yourself these questions:
Do I Have the Right Candidate?
Certain people -- let's call them "fastidious" -- don't like surprises. "I am one of them!" Dallas event planner Steve Kemble says. "I want to know everything about an event before I go." Also rule out anyone who gets really excited about milestones and birthdays. Trying to surprise these types is almost mean, he says: They'll just think you've forgotten to plan anything.
Do I Have Enough Time?
Ideally, that's six weeks for a party of 25 or more, says Kemble. One month out, consider reserving a room at a restaurant or bar -- a good idea if it's a place your guest of honor frequents, or that will best accommodate everyone. The biggest time sink, though, will be figuring out whom to invite (including any surprise guests!), then tracking down their contact info.
Am I Up to the Task?
Here's a dirty secret: "Many times the people being surprised find out; they just don't tell you," says David Tutera, host of WE TV's My Fair Wedding. Evaluate yourself as a potential host: Can you keep your cool? (Hint: Don't stop talking to your best friend two weeks before her birthday.) Are you prepared to improvise if things go off-script? If not, stick with a non-surprise party.
Get Creative -- Just Not Too Creative
"If you do something too funky, the person is going to know something's up," Kemble says. "If you go to Chili's a lot, say, 'Let's go to Chili's.'" When Kemble helped Lori, wife of Dallas Cowboys executive Jerry Jones Jr., with his surprise party, they chose to throw it on a weeknight at Cowboys Stadium, since he goes there for work anyway.
Preserving a surprise involves careful planning and serious covert ops. Herewith, your marching orders.
Enlist a co-conspirator. A trusted friend is a big help -- and crucial if you live with the guest of honor. In that case, direct calls and e-mails to your compatriot, so you don't get caught with evidence, like an RSVP on the home voicemail. Use the friend’s address on mailed invitations in case of undeliverables, and do the planning at your accomplice's house, or a restaurant or coffee shop. '
Time it right. "A great surprise party happens in the weeks leading up to the actual event," Tutera says. Your honoree is expecting it the day of the occasion. And after? You'll wind up with a peeved birthday boy who thinks you forgot or didn't make a big enough deal out of his day, Tutera says. (So, regardless, plan something on the real day, too.)
Get the word out. Phone calls, mailed invitations or a Facebook event notice work best, says party planner Johansson. You don't want people forwarding the info to random friends -- a problem with e-mail or Evite. (On Facebook, events designated "secret" can only be seen by selected guests.) Johansson suggests keeping the initial correspondence brief (date, place and time) and providing additional details only to those who RSVP "yes."
Put a day-of plan in place. You and your co-conspirator will have to split up: While one escorts the guest of honor, the other will play party host. (If it's at someone's home, no parking in the driveway!) The chaperone must let the party folks know when they're 10 minutes away and when they've arrived. Try calling the host's cell and letting it ring twice.
Consider the big reveal. There's nothing worse than someone "hiding" in plain sight or prematurely screaming "surprise!" Kemble suggests a practice run with guests. And no need for a crouching-behind-the-sofa moment. Tutera thinks a dark, empty room can be suspicious -- he prefers a party already in progress, with the honoree slowly realizing all of his loved ones are there.