Whether you are a beginner, who is just starting to grasp the basics, or an advanced student who can speak quite fluently, ESL (English as Second Language) learners make grammar mistakes. Although some mistakes don’t affect your ability to communicate, you should always work to increased accuracy. Some mistakes are more common than the others,here are the 5 biggest mistakes:

1- Choosing the Wrong Tense:

I have been to New York last summer. >> I went to New York last summer. 

In this case, you fail to notice that because you're referring to something that happened at a specific moment in the past, so you should use the past simple , not the Present Perfect. You may remember the correct form of the verb (and remember the correct past participle for a specific verb, for example); the problem is that you simply use the wrong tense to express yourself.

2- Confusing the Infinitive, Gerund or Base Form of the Verb:

I must to buy a new English book. >> I must buy a new English book

You often use the infinitive with modals like must, when you should simply use the base form of the verb. You might also use gerunds when you should use infinitives:   (I decided going to the park). >> I decided to go to the park. 

3- Misusing Adverbs and Adjectives: 

I want to speak English good.>> I want to speak English well. 

In fact, if you want to speak English well, you'll need to make sure your adverbs and adjectives are in tip top shape. 

4- Subject-Verb Agreement

People is coming to my party tonight. >> People are coming to my party tonight. 

People are people,but you often need to make sure the verb agrees with the subject of your sentence.

Basic Rule. A singular subject (she, Bill, car) takes a singular verb (is, goes, shines), whereas a plural subject takes a plural verb.

5- Wrong Word Order:

This happens mostly because you think in your native language - Turkish - which has a different word order than that of English. For example,The verb always comes at the end of the sentence in written Turkish,For example: Ben gazete okurum: it means Literally :“I newspaper read.”, but this would be a wrong sentence in English, so you have to say: “I read newspapers.”.

Finally, keep in mind that it's okay to make mistakes as long as you learn from them. I hope you found this article helpful.