Okay there is one really important thing to remember about recall: you are recalling the dog to something more exciting not stopping the fun they are having.
You must always have high quality rewards : this could be food if so never ever use kibble but use sausage, cheese, chicken, livercake etc. If a toy make it a really special toy that the dog does not have access to all the time.
The reward for recall needs to be higher value than what you are recalling from.
Do not recall if you cannot give 100% attention to the dog when it does recall.
Do not recall if the distraction is too much for the puppy (unless you have done a lot of distraction training ? more on that later)
So imagine the scenario you are having a glass of wine and a chat with a friend and you are called in to do the ironing, or you are doing the ironing and called over to have a glass of wine and chocolate ? which scenario would you prefer. It is the same for the dog.
When you do recall do not put on the lead everytime or do not only recall at the end of the walk, or when something fun is happening eg playing with other dogs.
When you do recall have a word/whistle you use each time (I do not use the dogs name but up to you) then run away from the dog still calling and when the dog gets to you go ballistic with praise treats /toys. You need at this point to give 100% attention to the dog and the dog only. Let the dog go off and play and then do the same again. Sometimes the reward for coming may be to let your dog go off and play with other dogs.
Vary your reward but it must be high value.
Never ever tell a dog off once it has come to you however frustrated you are feeling.
Prevention is sometimes better than failing so if you know that the dog will not recall prevent them from running off or just go and get them without recall (easier said than done at times)
Distraction training.
In a quiet place build up the exciting things your dog can be recalled from.
Depends on the dog but start with sausage on the floor, have your dog on a lead and walk towards the sausage so the dogs sees it then leg it in the other direction calling the dog (they have to follow an when they do give loads and loads of little bits of sausage so the reward is greater than what they have been recalled from)
Build up the distraction maybe when children are playing, eating, riding bikes, eating ice creams, talking to other dogs etc.
If you recall has really gone to pot, get a new recall word and start again say the word click and treat. do not let the dog off until you get 90% success rate. I am very scientific about this and do calculate my successes to a behaviour before I move on or take it out and about.
Recall is also building on the relationship you have with the dog generally, make every experience with the dog fun, being around you needs to be positive and fun, the clicker is ideal for this.
You will constantly have to work on recall for all the dogs life ? never take it for granted ? but it is straightforward the dog is recalling to something more exciting than it was leaving!