This is a controversial topic for a lot of dog groups, but I have a controversial dog so I think its fitting it gets talked about.
Your dog should 100000% be muzzle trained and be comfortable wearing a muzzle. I am fully aware that people think a muzzled dog looks scary or intimidating and people will often cross the road rather than walk by a muzzled dog. If you are reading this and feel this way, its time to update your thinking. Especially since at the heart of it, a muzzled dog is actually less likely to hurt you since it removes the ability to bit you. So just remember that the next time you walk past an unmuzzled dog.
The reason muzzle training a dog is so important is because you never know when you will be in a situation that requires you to muzzle your dog. For instance, if your dog had a medical reason it needed that muzzle (perhaps to prevent it from licking) do you think it would be easier to muzzle train that dog after the injury, or before? The dog is already in pain and is going to need time to adjust to that new muzzle - you'll be in a very tricky situation if you wait.
While I am not a trainer and you should always consult a training before taking on new training approaches, this is what I did to muzzle train my dog.
1. Have her sniff the muzzle. Get her used to how it feels, looks, and smells. You want them to investigate that new training tool and have them accept it. 2. Put the muzzle up against her face (don't put the muzzle on, just up against their face). Give them a couple treats with the muzzle still on to show them its ok. 3. Once comfortable, go ahead and put the muzzle on the dog (without tying it up) and feed a treat through the muzzle. After a couple treats, remove the muzzle from their face and feed another treat. 4. Put the muzzle on fully and feed a few more treats. I only kept the muzzle on for a minute before removing it and did this a couple times before walks.
For my dog, this didn't immediately make it so that she loved having the muzzle on and it didn't bother her. But it did teach her not to fear the muzzle (and she never tried to bite me while I was putting it on) and we continued to use it every day on our walks. Alan does require a muzzle for all her walks as she will bite dogs if she gets too close, so consistent use was key for us.
If you don't use a muzzle regularly I would encourage you to meet with a trainer right away to start using this tool. I have also included some resources below to help out.
Using a muzzle could keep other dogs safe from a dog getting too overwhelmed and reacting (which can happen to every dog, even if it displays no reactivity issues). If more people use a muzzle we could prevent so many "accidents" of dogs biting humans or other animals, and destigmatize muzzled dogs as something one should fear. Imagine how cool it would be to ensure the safety of all?!