Everything starts with and is influenced by learning to ‘talk dog’ and understanding your dog’s needs (both physically and emotionally).
Good quality socialisation and habituation, working at your dog’s pace, is so much more important than teaching traditional behaviours such as sit, down, etc.
On that note, a ‘sit’ isn’t as important as you think it is. And can matter of fact become an aversive for a dog with physical ailments. Don’t make it a default part of other behaviours you teach your dog.
Be your dog’s safe place and provide as much choice and agency as you can for your dog.
A happy tummy and gut makes for a happy dog!
Be more dog, you fur friend will love you for it.