Make a list of everything you will need to pull off your surprise: guest list, gifts, dinner plans, wine, photos and cake.
Establish both a contact person at the destination (concierge or restaurant manager) and a contact person on the guest list (sister, best friend). These key folks will aid in both the preparation and the distraction components of the surprise.
Have all of the actual arrangements made in advance of your arrival so there is little to prepare for once you've arrived. Last minute details and mishaps can be dealt with by your contact guest and the contact destination person.
Keeping your spouse in the dark too long is tough. You will need to come up with a reason to be at the place of the party at the time designated. Your destination person will guide your spouse away from or towards the party destination. Concierges are especially good for this task.
Delegate as much as you can. Have guests bring cameras to take photos and be in charge of gifts. Your job is to pull of the surprise and make sure everyone has fun!
