Dungeon crawling can be a fun way to game. Everyone pulls together a group of characters that are skilled in combat, traps, and burglary, and tries to fill all of the roles in the party so that they're not crippled by a lack of, say, area effect magic to take down swarms. Then they head out into an area where they go from place to place defeating monsters. The area may or may not actually be subterranean. The goal of this kind of game is pretty simply: Kill the Creatures and Loot the Area. There may or may not be an overall premise or theme. The monsters might be picked at random and placed on a randomly generated dungeon map. Tastes may vary. But there are still a few basic rules to bear in mind when you're playing this kind of game.
Relax. It's easy to get tied up in a belief that roleplaying must be a story heavy panorama. It doesn't have to be. All forms of roleplay are worthwhile so long as everyone is enjoying themselves. So don't worry if its canonical for two vampires, a werewolf, and a mage to join up and kill a random assortment of beasties in the London Underground. Is it fun? Then go nuts.
Know the Rules. You don't have to know all of the rules but do know what you can and can't do and what your skills and abilities do. If you want to stretch yourself, know the sorts of environmental benefits and penalties you can use to make things more tactical. Nothing grinds these games down to a halt more than if everyone has to keep checking the rule books.
Remember the Golden Rule. When in doubt about an obscure rule, let the Game Master make one up. While knowing how a feat actually works is important because it will come into play numerous times, it isn't necessary to know the precise Acrobatics DC of traversing a narrow and slippery slope.
OOC Conversation is Generally Okay. Since these games revolve around combat rather than IC conversations, it isn't necessarily disruptive to chat during the game. There are a couple of restrictions, though. Pay attention when the Game Master is describing something or when its your turn and don't chat to people when its their turn (hold your thought). Otherwise, it's normally okay to chat.
Know What You're Going To Do. Combats can bog down quite quickly if people wait until their turn to choose spells, look up rules, or figure out what they want to do. You've had everybody else's turns to figure out what you're going to do so be ready to do it.
So there you are. A few basic rules of thumb to help you enjoy your dungeon crawling experience. Hope it helps and happy crawling. May the loot be ever within your grasp!