1. Have an intrinsic motivation (interest in the specificity of the language itself) rather than an extrinsic one (perspective of making profit in China). If you enjoy learning a language, your mind and efforts will be more focused and you'll learn much faster. If you enjoy learning Chinese, just for the sake of it, just because you find it fun, it will be much much easier, and you will get much further. The more intrinsic motivation you have, the further you'll go.
2. Make sure you get the pronunciation right from the start. Use pinyin charts, and do repetitive drills, until you're sure your pronunciation is correct. Later it will service you well. You'll be able to hear the different accents, and create your own personal accent. You'll be able to sound either like a native, or you'll use your foreigner identity to forge your own accent. Mandarin is a tonal language of 4 primary tones, which means that speaking the same word with different pitch will give the word different meanings. Attempts have been made at Romanization (using of the "abc" alphabet) of Chinese words to assist with language learning. However, if you wish to speak Chinese with proper tones, it is highly recommended that you use an audio-based program and focus your efforts on reproducing the sounds that you hear. Romanized/written Chinese only provides an approximation until you become familiar with the actual sounds. So pinyin system is important, but less than audio-based practice.
3. Be aware of the negative transfer of mother tongues. For the learners who have already mastered the basic lexical items and basic grammatical structures of a language, foreign language learning is proceeding on the basis of the existing linguistic knowledge (of the mother tongue, of general learning strategies, or of the universal properties of language). Consequently, the grammatical and semantic knowledge of the mother tongue will have definite effects on the learning of the grammatical and semantic structures of the second language.
When learning a new language, you may often use approximate sound of the mother tongue instead of the Chinese phoneme and therefore make some errors in pronunciation. In addition, you may also be confused by Chinese grammar if you always do some inappropriate analogy according to what you have learned, since there are not strict morphological changes in Chinese and word order or function words are the main way of expressing grammatical meaning. It is thus important to remember that do not be too influenced by mother tongues when learning Chinese.
4. Learn the culture behind the language. Language always goes with its culture, so if you learn Chinese without an awareness of Chinese culture, your communication with native speakers will be frustrated. In addition, different nations have different communicative ways and discourse structures, which by every means, are sure to influence the new communicative ways and discourse structures on different occasions and to different degrees. For example, when Chinese say “哪里哪里” (literally where where), it does not really a question asking where to go but a kind of humble expressions to say “I am not that good and you are flattering me”. Getting immersed in Chinese culture will only do you good and increase your understanding of the language, which is, after all, a part of culture. After you have basic understanding of the way Chinese people communicate, you will better grasp much conventional usage of words that have different meanings from what they seem to be.
5. About Chinese characters. It has been discussed for a long time that whether non-native Chinese learners should learn characters. In my opinion learning characters is essential to learning the language beyond the basics. In fact, I feel that aside from pinyin and good pronunciation, learning to read/write is the next most significant step to boost your rate of learning Chinese. A lot of people think that the spoken word is enough - they just want to be able to communicate, not write novels in the language. In the case of Mandarin, learning the writing system can actually be beneficial - it will reinforce your knowledge of the language. Learning how words are written will allow you to spot similarities with different words that contain the same character, making it easier to remember. A lot of instructors claim that, on the long run, learning to read Chinese makes it easier to learn the language, not the opposite. Of course, there will be a bit of a learning curve when you start, but before long, reading/writing will be a huge supplement. You will be able to read signs, menus, books, movie subtitles, and textbooks. Perhaps most importantly though, you will be able to use Chinese websites and social networking services. All of this will help you quickly expand your vocabulary and zoom in on areas that are of real interest to you.
6. There should be more key factors for non-native Chinese speakers to learn Chinese, but once you have the right motivation, get the pronunciation right, and have a clear idea of what you are going to learn (like culture and characters), it is just a matter of time. One last thing is to find the right tools and texts which serve you need and a good teacher will also guide you to the right path. Seize the every opportunity to practice Chinese and make it part of your life. Sooner or later, you will love learning Chinese and find yourself improve a lot.