Oh God. Another movie about a dentist.
When have you ever heard that? There aren't movies or books or TV shows about dentists. That's why, if your main character is a dentist, your book will be an instant bestseller.
We don't want to hear about more Han Solos or more Dirty Harrys. (Han Soloes? Dirty Harries?) We want fresh meat. If your book's main character has any of these jobs, it will be bad and you should feel bad.
Mercenary or traveling badass
...Or one of his relatives
Last member of an ancient order/race of people with cool powers
What other jobs are you sick of seeing?