Every pack has rules, so I've listed the most common ones. Of course, these may differ.
No godmoding or powerplaying - this means, in simple terms, no making your wolf invincible. This is possibly one of the most important rules. For instance, if your wolf is in a fight, you cannot make it dodge every move, and neither can all of its attacks hit. Also, you cannot RP about what happens to another wolf. This may seem simple enough, but you'd be surprised how many people don't understand it. So, you cannot put something like *Mirror bites down on Rainfall's leg, snapping the bone.* What IS acceptable would be: *Mirror bites at Rainfall's leg.* Then Rainfall may reply: *Rainfall dodges away quickly* or *Rainfall tries to doge, but not quickly enough, and his bone snaps in Mirror's mouth.*
No killing of other wolves - exactly what it says. If you are in a fight, they may choose to kill themselves, i.e. saying that they die from the wounds you give them.
No swearing - you don't need much of an explanation. Most RPers are still at school, so swearing is not acceptable in most places
No graphic wounds or breeding - again, it comes down to the same thing as swearing.
No fighting with Alphas - this is because most Alphas are the owners of the site. They may choose to put their rank up for challenging, but it is not likely. You cannot ever overthrow Alphas.
No unrealistic colours/ additions/ magic etc. - your wolf cannot be purple, have wings or fly. Something to that effect. Elemental wolf packs, however, do allow and encourage this. You'll have to check the pack rules yourself for this one.
Alpha's decide the decisions of all fights - this, too, is present in most packs, but not all. It means that any fights you have will be judged by Alphas, and no one else, unless one of the fighters chooses to lose. You cannot choose to win, as this is unfair to the other wolf.
Fight only in the designated ares - most packs have a fighting area. This is to stop the pack becoming chaotic. It is hard to work out what is happening if everywhere you go there are wolves fighting. Some packs do have disaster boards, and there may be times when the pack is unstable that it will be announced here that you can fight anywhere.
You must obey all those of a higher rank - we'll be coming to ranks later. Wolves with rank have usually earned it through either the wolf being loyal to the pack, or for the RPer being active. The latter is the most likely.
Be active - this is another very important one. Some sites will delete your accounts if you do not post for a certain amount of time. If you are going on vacation, or do not have time to post for a while, contact the Alpha saying so. A pack that has few members but is active is much better than a pack with loads of members but is not very active.