Tug away, but make sure you have some rules.
Tugging with your dog, by itself, won't make your dog a dominant aggressive uncontrollable dog. Rather, you'll find here that many of us use it as a reward in training (we give a command, the dog complies, we give the dog a release command and he gets a nice game of tug, rinse and repeat). However, I always tell people it *could* lead to pushy behavior so there have to be rules. Our rules:
1. The dog must out when I tell him to (you'll find lots of threads here on teaching the "out")
2. The dog must be careful not to bite our hands, clothes, etc (simply say no, end the game or give a "time-out" from the game if he does and he'll quickly learn)
3. The dog cannot initiate a game of tug by himself (be careful because if you reward them initiating the game you can end up with a dog that sticks tug toys in your lap all day). Sometimes we let the dog believe he initiated the game but usually we start and end the game
4. (probably optional, but I would try to enforce it anyway) When the dog wins he should push the tug back into you to play more rather than take it and play keep away. The best way to do this is simply have a leash in your hand while you play so he can't just run off with it
In a nutshell, that's it, but I would probably look around these forums or watch any videos by Ivan Balabanov (canine training systems) or Michael Ellis (Leerburg) to get a better picture of what a game of tug should look like
Hope this helps