Put together two bags full of Halloween treats. These treats can be very general - candle holders, knick-knacks, candy, etc. Dollar stores, the bargain bins at Target, and the Halloween section of craft stores are all great places to shop. If you know exactly who you want to ghost you can make the bags a little more specific. For example, this year we "ghosted" a neighbor with a 2 year old son and we put a few matchbox cars in there and some goldfish crackers in lieu of candy. The bags do not have to be expensive. This year they only cost us about $10. It is more the fun of the activity then the value of the bags that makes the game what it is.
Print out the ghost letter and put one in each bag.
Make two paper ghosts. We put the tape on them so they are ready to just stick on the door right before we leave the house.
Pick two people to ghost. After dark, and only with an adult, stick the ghost on the door, the bag on the front step and ring the doorbell. Run away so you don't get caught!