The Mastiff is an intelligent dog and they like to please. However, their training has to start as early as possible when dogs are still manageable size-wise. Their training has to be consistent and always fair so that dogs understand what is expected of them. Puppies need to be taught the "basics" as soon as they arrive in their new homes and then once they've had all their jabs, it's a good idea to enrol them into puppy classes. Not only is this a great way of socialising a dog, but it's a good way to start their education in earnest in a safe and controlled environment around lots of other dogs and people.
Training sessions need to be kept short to begin with and they have to be as interesting as possible to keep a puppy or young dog focussed on what is being asked of them. Longer, more repetitive training sessions make it harder to keep a dog's attention. Being sensitive by nature, Mastiffs do not respond well to any sort of harsh correction or heavier handed training methods. They do answer well to positive reinforcement and high value treats which always brings the best out of these impressive looking dogs.
Mastiffs need to know their place in the pack and who is the alpha dog in a household or they may take on the role of dominant dog which is something to be avoided at all costs with such a large and imposing dog.
