First of all you will need at least 10 or more people to be the "aliens". These are people who are willing to hide up trees, behind bushes and under benches in the pitch dark for the duration of the game. The rest of the group should be divided into teams named after colours, i.e. Blue team, red team, yellow team, etc. About 5-6 people per team is good. Each team must have one flashlight, which they should try to use as little as possible so as not to give away their location to other teams, especially when finding one of the "aliens".
Each Alien is given into his or her possession, in addition to other objects that you can decide upon, several of those light sticks that are activated by bending them in half. Assorted colours are needed, one for each team colour, i.e. blue, red, green, yellow, orange, purple, etc. Also a number of the stripey light sticks are needed which are worth bonus points.
The aliens should change their positions frequently making them more difficult to find by the teams.