All students are different and yet, there are some mistakes that are very common among Chinese learners. Here are six common mistakes I can share with you:
Adverbials (especially of time and place)
Foreign learners of Chinese often have difficulty in dealing with the position of adverbials in a sentence. Influenced by their mother tongues, learners often place adverbials at the end of a sentence. For example, they translate the English sentence: "I found a wallet in the park." into "我发现了一个钱包在公园里". But, this is incorrect. Another example is, "My mother goes shopping every Sunday morning" into "我妈妈去购物每个星期天早上". This is also incorrect.
对汉语学习者来说，状语在句中的位置通常是个难题。受母语的影响，他们经常将状语放在句末。例如，他们会把英语句子"I found a wallet in the park"翻译为"我发现了一个钱包在公园里"。但这种翻译是错误的。还有一个例子，他们会将英语句子"My mother goes shopping every Sunday morning"翻译成"我妈妈去购物每个星期天早上"。这种翻译也是错误的。
These two Chinese sentences are incorrect; they are not what Chinese people say in their everyday life, although they can understand them if you say the sentences to them in that way. Native Chinese speakers can immediately tell the speaker is not a native speaker even if his or her pronunciation and intonation are perfect.
The right way is to place adverbials, especially adverbials of time or place, is immediately before the verb of the predicate. So, the correct ways to say the above sentences are: "我在公园里发现了一个钱包" and "我妈妈每个星期天早上去购物". These are correct!
Order of time and place adverbials
When there is both an adverbial of place and an adverbial of time in one Chinese sentence, foreigners tend to put them in a wrong order. They put the adverbial of place before the adverbial of time, but Chinese people do the reverse. For example, I heard someone say: "我在中国去年夏天学习汉语了". The correct sentence should be: "我去年夏天在中国学习汉语了".
Chinese people place the adverbial of time before that of place.
Interrogative or Question Words
Some learners place interrogative words, such as who, where, when, what, why, how, etc., at the beginning of a sentence. This is an error. For instance: "谁你邀请来参加晚会？" and "怎样你去北京的？" are both wrong.
Chinese speakers just use the declarative word order, and they don't have to place the interrogative words at the beginning of a sentence. So, the correct word order should be: "你邀请谁来参加晚会？" and "你怎样去北京的？".
谁 is an object in the sentence, so just put in after the transitive verb. And 怎样 is an adverbial in the sentence, so just place it before the verb.
Let's talk about the right use of the number two in Chinese. Native Chinese speakers say the number two in a couple of ways, which are èr and liǎng. When the number is followed by a noun, we use liǎng. If not, we say èr for the number two.
We say, 余数是2 (èr) and 我喝了两（liǎng）杯牛奶。
Check out a post before about "二" and "两" for details: Differences between "二" and "两"
不 (bù) and 没 (méi)
Some learners use the two negative words, 不 (bù) and 没 (méi) inappropriately.
不 (bù) is used for the subjective will or wish, while 没 is used to tell an objective fact or statement. For example, Chinese speakers say: 他不想去英国。他没去英国。These mean: "He doesn't want to/won't go to England." and "He did not go to England."
What's more, 不 (bù) can be used in any tense–present, past and future, while 没
(méi) cannot be used in the future tense. For example:
"I did not like, I don't like and I won't like… rock and roll music."
"I did not look down upon him; I don't look down upon him now, either."
Here is another post about "不" and "没有": How to say "No" with "不" and "没有" in Chinese
不 (bù) can be used before all auxiliary verbs, but 没 can only be used before secular auxiliary verbs. For example, we say, 不喜欢，不想要，不应该，不可能，没能，没可，没敢. In addition, 不 (bù) can modify both adjectives and verbs, such as, 不喜欢，不漂亮， while 没 (méi) can only modify verbs, such as, 没出发.
The above-mentioned mistakes are very common for foreign learners of Chinese. If you can decrease and then eliminate these mistakes, your Chinese will sound much more natural.
Translated from: italki