When dogs meet, a wealth of information passes between them through their scent glands between their toes, behind their ears, above and below their tails together with lots of body language. You should get to study and understand their body language and know what to expect of them. Initial meeting will usually be face to face. Next move can be the back of the neck, and if that is acceptable, all is good and they will then try down the leg and undercarriage to the top and under tail. If the dogs pause with stiffening muscles while smelling the back of each other's necks, there will probably be a confrontation. Note the Photos of the German Shepherd and the Terrier opposite.
There is one key signal between them that I look for all the time, and that is the "equals sign" shown in the photo opposite. It will often be demonstrated after the initial meeting or a confrontation, showing that they have come to terms with each other.
I often refer to my "equals sign". That is when the two dogs' bodies go parallel with each other looking in the same direction. It may only be witnessed for a second or two or it can be extended. Sometimes the dogs go bounding together in this way, I'm sure you have seen that. Sometimes one is wanting to show it, and the other not, or not accepting, and the dog wanting to demonstrate will keep throwing their hip in while rotating clock or anti-clockwise. When the 'equals' position is accepted between the dogs, they can play and rough and tumble and no harm will come to them. Good fun!
Is your dog fearful of meeting other dogs even when you know that they are friendly?
The trick is not to encourage your dog to meet at all, just the opposite. You need to meet the other dog, and very, very importantly don't at any stage even glance at your dog. So pat and pat and pat the strange dog, thinking only of it. The chances are very high that your dog will come up behind you looking for support. Continue to pat the new dog and ignore your own dog. Your dog might carefully go up to the other dog's nose and sniff, but is more inclined to go to the back of the other dog to sniff it's back end glands.
A great lesson for all, as long as you never look at your own dog.