The Tibetan Mastiff was bred primarily as a guard dog and is highly loyal, protective, independent, and yes, stubborn. Keep in mind that these beautiful dogs tend to be quite territorial and require a strong fence to keep them on the right side. One of the best things you can do at the very outset to help keep him calm at all times is to socialize him with lots of other people, dogs, and situations. This will help him to be more accepting of new situations, including grooming.
Like many other breeds, Tibetan Mastiffs are not fond of new situations and the sight of the various brushes and tools you will use to properly groom him are likely to make him more than just a little nervous. The good news is that while he is young you can train him to remain calm before and during grooming. Along with this, most Mastiffs become extremely calm animals as they mature.
Size can make a big difference when it comes to grooming a dog; the last thing you want is a 180lb Tibetan Mastiff who is too wound up to groom. Use the time spent training your pup to calm down as the perfect time to bond with your pup. Keep him groomed each week. If you let it go too long, his hair may become heavily matted and have to be cut instead of brushed.