Word order is of a great importance in Vietnamese language. It is a non-inflecting language and it relies on word order and function words to signal function meaning. The verb "to be" is hardly ever used because Vietnamese adjectives contain their own verbs.
As a quick example, take a look at the sentence below:
English: This person is old.
Vietnamese: Person this old.
Vietnamese word order follows the English word order in the following situation. In all other situations the Vietnamese word order differs.
Vietnamese word order influences the Vietnamese speaker of English. Understanding why a learner (or a group of learners) make(s) mistakes, helps you as teacher to approach and present the topic in a better manner.