Locksmithing is a specific discipline with a broad range of set standards and techniques for dealing with lock issues. Hence, any locksmith has their own way of handling locked doors. There is no specific process one expert uses to open a locked door.
Nevertheless, one of the most popular ways locksmiths utilise is their picking kits and using the appropriate tools. But again, pick kits are personalised, so the more comfortable the locksmith is with the equipment, the faster the problems can be solved.