One of the biggest mistakes I'm seeing in my classes and in puppy playtime: dogs making noises are not always being aggressive. A lot of dogs, especially a lot of terriers, play very loud! Learn your dogs' body language, that is going to tell you more than the noise they are making. Read books, watch videos, and most importantly, watch your own dog for other signs of aggression.

For example:
Stiff corners of the mouth
Stiff body, stiff tail
Head over other dogs' body (this is a very dominant posture)
Ears pinned back to head
Fur standing up

But ultimately, do your research, work with your own dog. Dogs will and can growl while playing or trying to play. Work with a trainer if you're unsure of your own dog.

On the other end of this, if your dog is feeling aggressive, and growling, that isn't something you want to discourage! If your dog is growling, that is their way of saying "Help! I'm uncomfortable in this situation!". If you tell them "No!" "Stop!" Etc, you aren't making them comfortable with the situation, you're stopping them from warning.

For example, if your dog is afraid of nail trims, and growls when you touch their feet. If you discourage their warning, they can't tell you they are uncomfortable. So they have no choice but to let you poke and prod at them until they can't take it anymore and say "ENOUGH!" and snap at you. Instead, change the situation! Treat for touching their feet, take baby steps, make them comfortable. Don't take away their warning.