My dog is reactive on walks, what should I do?

my gsd use to do the same thing. i began training him to sit/stay or down/stay until the people and dog would pass. it took time and patience but he eventually got it and now when he sees a dog approaching, he will either go into a sit or down position and wait until they pass. if he gets up make him sit again. he is on a retractable leash and I keep it all the way retracted so I have control of his head and body. if he gets up, i immediately give a correction and make him sit back down. if he starts to bark, he gets a correction. if he does anything except stay in the sit or down position he gets a correction and gets put back into that position. we wait until the person passes, then he is allowed to proceed on the walk. if he starts to go back in the direction of the person and dog who passed, he gets a correction and goes back into the sit/down position until he settles down. you do this every time you pass someone whether they have a dog or not. it took me several weeks to get him past the lunging barking thing, but with patience and persistence he learned and we now can walk right by any dog or person without so much as a look in their direction.