I forgot to answer your question OP. we just went very very slowly, at the dog's pace. super quiet and chilled at first with no expectation to do usual doggy stuff like walking nicely on a lead or understanding commands.
One of ours hated walking on the roads, so for a while we drove him to quiet country spots where he could sniff and wander as he wanted, let him set the direction and speed. after a couple of weeks we gradually tried him on the roads again and he was totally fine, just tiny steps at their pace. we never rushed or pushed, just let the dogs lead.
My reckoning was we had the rest of all time to train, so we just slowly and gently tackled each new thing as it became needed.
the first few weeks / months were toilet training and settling quietly while i was working. then building up confidence for walking. lots of pub training as that was very important to us, but that incorporated the settling quietly, relaxing around other dogs, so step by step they learned what we wanted from them. we did A LOT of quietly sitting at a distance and observing. short spurts of that, no expectation they would sit and watch for ages, but short, repeated spells whenever possible, of roads, of people shopping, of dogs running about the park. it sometimes meant we'd go somewhere and leave again 5 minutes later but that's what worked well.
i will say both of ours were really easy to train and pretty intelligent. i read a lot about "street dogs" and there are interesting histories and traits which really made sense (look up the history of Romanian street dogs, it's really sad and they are the result of Ceausescu's clearance and displacement of people who had to flee and couldn't take their pets). Whereas Cyprus has a different history of using dogs for hunting and discarding those who are no longer useful. both of ours are pretty true to those scenarios.
I would read as much as you can about body language, it's really important to be tuned into what your dog is saying about their level of comfort but also where they get their outlets. this is something which is a bit more complex with a very mixed breed - you know what a Labrador or spaniel or Pomeranian was made for and how to satisfy those traits. with a dog on unknown heritage you need to spend a bit longer figuring out their needs and how to satisfy them.