The following are Spectacular Death's "rules" for groups and loot. This is NOT what is generally done in high end instances. For raids, we have adopted an "If you can use it, need it" looting system. This means that if a piece of gear drops that is useful to you, whether it is an upgrade or for transmog purposes or if it is BoE and you would like to sell it, you may roll need on that item. Toons for whom a piece of gear is an upgrade take precedent in need rolls over transmog or sellers.
1.) Establish loot rules BEFORE you enter the instance. Many instances have ore or herbs or skins. Always ask before the instance who has professions that could benefit from the run. Roll on these items to establish who gets which skins, herbs, nodes.
2.) If an item is an upgrade, speak up. KNOW YOUR GEAR. It is acceptable to ask, "What do you think? Is this an upgrade for me?"
3.) Always be polite. "May I need this?"
4.) If you need a piece and someone else does too, be gracious about either winning or losing the item.
5.) If you have won one piece of gear in an instance, it is considered good form to pass on other pieces unless no one wants the gear. Then, you may ask for it. This is particularly true if you are running content for transmog items.
6.) Remember, just because it's max levels running you through a low level instance, don't assume all the loot is for you. They may be looking for a transmog drop, money, enchanting materials or whatever. Always ask.
7.) THERE IS NO NINJA LOOTING PERMITTED IN THIS GUILD UNDER ANY CIRCUMSTANCES. NO EXCEPTIONS.
These "rules" are common sense and can be adapted to each instance. Communication between players before the instance starts goes a long way toward averting any loot conflicts.