What Types of Motivation are Key?

External factors such as good teachers and helpful textbooks, studying with other motivated language learners and being surrounded by effective senior colleagues, meeting frequently with friendly & encouraging local people, supportive organizational leadership and being given helpful advice on how to learn Chinese will all help one's Internal motivation.
Yet there are two other types of internal motivation that should also be fostered: Intrinsic motivation and Integrative motivation:
Intrinsic vs. Extrinsic Motivation
Intrinsic motivation is motivation from deep within the student. I read a book for pleasure. Intrinsically motivated students study Chinese because they want to study. The material is interesting, challenging and rewarding, and the student receives a great sense of satisfaction from learning.
I'm extrinsically motivated when I study Chinese in order (e.g.) to prepare for the next exam.  Extrinsically motivated students study and learn in order to receive a reward, such as the HSK certificate.
The difference in focus between intrinsic motivation and extrinsic motivation is that one is on one's ever-increasing ability to communicate in Chinese well and the pure inner delight this brings, the other is on the external reward (e.g. HSK certificate) and the sense of pride it gives me.
Integrative vs. Instrumental Motivation
Integrative motivation (people-focused) is characterized by the learner's positive attitudes towards Chinese people and the desire to integrate into the Chinese community.
Instrumental motivation (goal-focused) underlies the goal to gain some social or economic reward through second language achievement (e.g. passing the HSK exam so that I can study in a Chinese university or apply for a job), thus referring to a more functional reason for language learning.
During full-time language learning, you should try to foster Intrinsic motivation as well as Integrative motivation as both these will help you want to continue acquiring Chinese long after full-time language study is over.