The amount of glucosamine you should give your dog depends on their weight. The general rule is that you should give your dog 0.5 grams of glucosamine per pound of body weight per day, so for a 30-pound dog you would give them 15 grams per day (0.5 x 30).
Make sure to always measure the amount carefully using measuring cups or a scale; if you don't use enough then it won't be effective, but if you use too much then it could have negative side effects like diarrhea or nausea!
It's best to check with your veterinarian for specific instructions based on your dog's weight.