Teams
Play the traditional way by having teams of people. Four to six people per side is a good number. You do not want too many people on a team or they will be tripping over each other. Vary the team game by rotating people in and out if you have too many people playing. For example, start with four people on each team; the extra players stand on the sidelines. After each serve, the team rotates. The new member is the server and the one of the court that served first in the rotation is out.
Blind Badminton
Blind badminton is fun, especially for children. Cover the net completely with a blanket or two. Make sure that neither team can see the other side. This makes the game a little more difficult by not allowing the teams to actually see when the birdie is coming in their direction. Score points in the traditional way. Play to a total of 10 points.
One at a Time
This variation of badminton is a good idea for older kids and adults. Every one should be divided up into two even teams. Each team member will play, but only one at a time. One team serves, as soon as the server hits the birdie he needs to leave the court and the next player comes on. The player on the opposite side of the net returns the birdie and leaves the court while a new player enters. Keep volleying back and forth, switching players after each hit. No player is allowed to hit the birdie twice in a row. If they do, the other team gains a point. The first team to reach 10 points wins the game.
Birdie Blitz
Divide your players up into even teams. You will need one birdie for each player. It is also necessary to divide the court up into as many sections as you have players on each side. Four squares are good when you have adults playing, but for children separate the court into six sections for six players. Use string and tent stakes to divide up the courts. At the start of the game each player hits their birdie. The object of the game is to keep all the birdies out of your square. This game is played just for fun and there is no need to keep score.