G.34.1- Occasionally, the game has something occur simultaneously. This means it is an "indivisible and unordered action". [D'Angelo 1998/02/03]
G.34.2- If something is to be done simultaneously with something else and both things have decisions to be made, all decisions are made before you do anything. Then you do all the simultaneous actions. For example, untapping cards during untap is simultaneous, but you might have to decide what to untap. If so, you decide before you untap anything. [D'Angelo 1996/08/01] As usual, if both players have decisions to make, the active player decides first. [DeLaney 2000/01/13]
G.34.3- If more than one permanent enters play simultaneously, then the order in which the effects of those cards enter play needs to be determined. This most commonly occurs when cards "phase in" (see Rule G.27.5). The ordering follows these rules: a) The active player decides the ordering among all cards which are not local enchantments. b) If cards have local enchantments on them, the effects of local enchantments on a card enter play after that card's effects, but prior to any other card's effects. c) If there are multiple local enchantments on a card, then the effects of those local enchantments enter play in the order in which those enchantments originally entered play. [Aahz 1996/12/04] For example, a Sandbar Crocodile is phased out with Flight and Earthbind on it (cast in that order). Feedback is on the Flight. When it phases in, the Crocodile's effects are considered to enter play first, then Flight's effect, then Feedback's effect (since it is on the Flight), then Earthbind's effect.
Note- See Rule Z.3.3 for information on simultaneous placement in the graveyard.
Note- See Rule Z.6.6 for information on simultaneous placement in the library.