Step 1: Rules
Step 2: The Playing Field
There are a few attributes that a playing field should have:
Concealment: The field should have plenty of places to hide. Wooded areas and parks are good for this reason.
Lack of Obstructions: Electric fences and rampant poison ivy or pricker bushes tend to make games less fun.
Not on Private Property: Don't trespass. Only play where you have the owner's permission.
Not Too Small: If the playing field is too small it's too hard to hide.
Not Too Large: If the field is too large you'll never find the hiders. The larger the field, the more seekers you should have.
Step 3: Tips for Hiders
Don't Stay in the Same Spot: It's OK to stop and hide, but staying in the same spot for an extended period of time is just asking to be caught.
Outmaneuver the Enemy: If the seekers figure out where you are, try to stealthily work your way around them and get away. If they spot you and chase you, try weaving in and out of trees, you might get lucky and lose them.
Avoid Crossing Open Areas: When moving from place to place, try to take the route with the most concealment, even if it's slower.
Don't Wear Yourself Out: Heavy breathing will give you away, and you'll need your energy to outrun the seekers when they spot you.
Step 4: Tips for Seekers
Surround the Enemy: Work together with other seekers to try and corner the hider(s).
Stay Together: Split into small groups or pairs to cover more ground, but avoid searching alone. If you do spot a hider, it's harder to outrun two people than it is to outrun one.
Make Use of Trails: Move along trails and open spaces when possible, unlike a hider, speed, not concealment, is your greatest weapon.
Watch for Movement: You're more likely to notice movement or sound than you are to actually see someone.
Step 5: Variations
In a Crowd: At a concert, street festival, or any other place with lots of people. Just be sure not to trample anyone.
At Night: Best just as the sun is going down so it's somewhat dark, but no one runs into anything. Everyone gets a flashlight.
Airsoft/Paintball: Instead of tagging the hiders the seekers shoot at them. Hiders can shoot back, but have smaller weapons (pistols).
In a Room: Everyone stays in one room and the seekers wear blindfolds. A true test of coordination.
Replacement: When a hider finds a seeker they switch roles, with the seeker (now the hider) hiding in the same spot.
Zombies: Seekers must extend their arms and growl "Brains! Brains!" throughout the game, unless they are vegetarian zombies, in which case they would growl, "Grains! Grains!"
Helper Manhunt: Like helper tag, if a hider is tagged they become a seeker. The game goes on until everyone is a seeker (thanks nf119).
Tournament: Uses two even teams which alternate being hiders and seekers for a set number of rounds, with each round having a time limit. If a round ends and all hiders have been found, the seekers win that round. If all the hiders have not been found, their team wins the round. Which ever team wins the most rounds wins the game (thanks lemonshark10).
Muggles: Hiders are not only out if found by a seeker, but also if they are found by someone who is not playing, also known as a muggle (thanks lemonshark10).
Journey: Hiders have to move from a starting point to a base on the other side of the playing field. If they reach the base without being caught they are safe. Instead of the last person to be caught picking the next round's hiders, the first hider to get to base picks (thanks othertonywilson).
Long Distance: Played in a large playing field (4-6 square miles), seekers are allowed to use cars, however, they are not allowed to run over the hiders or any pedestrians who get in the way of the game (thanks othertonywilson).
Partners: Hiders get partners and must stay together or they are considered to have been caught. Also, if one person gets tagged, their partner is also out (thanks tac135).
Jail: When hiders are caught, they get sent to a designated "jail" and must stay there until they are tagged by another hider, or a set time limit expires (thanks KillerPanda).
Sardines: Seekers who find a hider must hide with them, sometimes resulting in a large mass of people hiding behind a tree (thanks "byaaface").
Sasquatch: Hiders may jump out and tag a seeker, thus making the that seeker the next hider, or sasquatch. When a seeker finds a hider, they must yell "sasquatch," at which point the seekers may all run back to base, making the last seeker to reach base the next sasquatch (thanks jmicko).
Anything Else You Can Think of: Underwater? In zero gravity? The possibilities are endless. Post your ideas in the comments section and I'll add the ones I like best to the list.
Thanks for reading! I hope you've enjoyed this Instructable.