Upon first entering I usually make a circuit around the outside of the actual building. There's wolves in some of the side alcoves, and there's an ogre, a worg and a couple goblins guarding the other exit.
Once I've cleared this area I go back to the norther doorway into the building. There's a wolf and a goblin in the first room. The next room has a pit in the middle, and some goblins, some wolves and an ogre standing around. Once I've dealt with them I check out the southwest corner of the room. There's a few mediocre items on a bench, and a lever in the corner, which I wait to use.
Now go check out the doors on the east side of the room. They both lead to bedrooms, and each bedroom has a couple goblins in it. The bedroom to the north also has another small room in the back containing a lever, which controls the portcullis to the Goblin Mine.
Once you're back in the room with the pit go through the southwestern door and you'll find yourself in an area with a few worgs. After dealing with the worgs go through the door to the north and you'll have to fight a few goblins, including the Goblin Chieftain, who drops a Chieftain Charm.
Now go pull the first lever I told you about. It controls the portcullis out of the worg's pen. Finally, check out the rooms on the southern wall of the room with the pit.
The first room contains an augmented robe (+10% Protection from Melee Damage) and a Safe Travel spellshard, among other things, but you need either Dispel Barrier Lv.2 or a Piercing Crystal to reach them.
The second room has a couple ogres in it, one of whom occasionally drops an Iron Greatsword. Check the chests for items. The southwest corner of this room has a secret passage. Upon first entering the secret passage, check the chests for some coins and an Iron Greatsword. Now head down to the passage to the west. You'll have to disarm two traps in here. The secret passage exits into the Worg Pen. Now head over to the exit leading up to the Goblin Mine. You'll find yourself fighting a last stand battle outside the mine, and once that's over you can loot the mine for some coins.
Attempting to enter the Goblin Mine from outside is impossible, since the goblins hold the high ground on that route, so the only entrance is really through the Wolfrider's Warren.