scumbugs

No wishing to win a competion.
No wishing to interfere with or create true love,
No wishing for the things Anti-Fairies and Pixies do.
Fairies can't directly kill, maim, or injure living beings (but their magic can if it is done indirectly).
No traveling to the month of March, 1972 (only applies to Timmy Turner).
Nobody can see Anti-Fairies without the use of Anti-Fairy Goggles (until the events of "Jimmy/Timmy Power Hour 2: When Nerds Collide", Jorgen changes the rule to say they CAN be seen easily by humans as an insult to the Anti-Fairies).
If no kids in the world are miserable, Pixies can grant wishes (in this condition, all the fairies on the earth will be pulled back to Fairy World).
No wish for their fairy to have a baby (it was made a rule after Cosmo was born, but Jorgen never officially put the rule in the book).
A child can't wish to know if any other kids have fairies, or who has fairies. You have to find out by yourself (proven in "Fairy Fairy Quite Contrary").
A child can't wish to take away the fairies of another child. They have to be wished away by the same child, or compete in a Magical Duel.
Fairies only grant wishes to miserable children of the dominate species of Earth.
Yoo Doo dolls are very dangerous (however, you can still poof up Yoo Doo dolls).
Magic can't be used to win a contest, only for showing off (unless it is a Magical Duel).
No 'Super' wishes. (Not in da rule book, but a small rule created by Cosmo and Wanda for Timmy.)
When a child reveals the existence of their fairy or fairies, all witnesses and the child have their memories wiped, and all magic items they have come in contact with disappear. This is the largest rule.
No wishes that interfere with true love in any way unless asking Cupid.
No wishing that someone was in love with you unless asking Cupid.
Cannot wish for Christmas occurring every day (rule was caused by Timmy In "Christmas Every Day").