Always get his attention first by using his name in conjunction with the command. I sometimes start with "Layla, Watch Me!" to prep her for a command. You train "Max, Watch me!" by holding a yummy treat up beside your right eye. Max will focus on the treat and automatically make eye contact.After much work woith this, Layla got to the point where just the command focuses her immediately -- after all, there might be a treat!!
Just keep working, always making sure that when you use whatever command you want to be the "Come" command ("Max, Come!"), that he is on a leash or rope and ALWAYS has to follow through. Layla didn't "get" come until she was fully a year old. Once she got it, though, it was solid!