Instructions:

Make sure the birthdayboy or girl doesn't have a clew.

To make sure, let somebody pick him/her up from work, school, or anything.

Make sure everybody is there in time, plan everything properly.

Make sure the decorating is finished before the birthdayboy or girl walks in.

All the traces must be removed, so take away all bikes, etcetera from the backyard, or else he/ she will notice there are people in the house.

Make sure it's dark the time he/ she arrives.

Make sure there's somebody sitting next to the lightswitch, by the time everybody screams: 'SURPRISE!'.

Enjoy your party.