Always make sure your surfing has been approved by all roommates.
Decide the length of your surf before you stay, if possible.
Discuss any costs your surfing may incur and agree to pay them. Otherwise, be kind and offer some money for hydro.
Keep your things in your bags and out of the way. Make or put away your "bed" as appropriate.
Bring earplugs.
Don't hang out all the time... people tire of not being able to relax on their own sofa. Find a book and a coffee shop. Work extra hours. Hang out with other friends.
At the same time, don't avoid being there altogether. That makes it seem like you're only using them for their sofa.
Cooking dinner for the household never hurts.
Neither does doing dishes.
Be considerate with your usage of amenities and energy. Don't hog the TV. Don't leave lights on.
If possible, avoid eating household food.
This list of guidelines has been carefully tested by yours truly over the past month, and is guaranteed to make your sofa surfing experience a more pleasant one.
Soon I will have a home... soon I will have a home...