Three common grammar mistakes that non-native speakers often make:

Misuse of Articles (a, an, the):
Non-native speakers frequently struggle with when to use definite (the) and indefinite articles (a, an). This often stems from differences in article usage between their native language and English. For example, in languages that don't use articles, such as Russian or Chinese, learners might omit articles altogether or use them incorrectly. Additionally, determining whether to use "a" or "an" before a noun based on the following sound can be challenging.

Example: "I saw the movie yesterday" (correct) vs. "I saw movie yesterday" (incorrect).

Subject-Verb Agreement:
Maintaining agreement between subjects and verbs can be difficult for non-native speakers, especially when dealing with complex sentence structures or irregular verbs. This can result in errors where the subject and verb do not match in number (singular/plural).

Example: "The book on the table is mine" (correct) vs. "The book on the table are mine" (incorrect).

Incorrect Word Order:
Non-native speakers often struggle with word order, particularly in constructing questions, forming negative sentences, or using adverbs correctly. Word order varies across languages, and this can lead to errors in English sentence construction.

Example: "She usually goes to the gym on Saturdays" (correct) vs. "Usually she goes to the gym on Saturdays" (incorrect).

These mistakes are common among non-native speakers, but with practice and exposure to the language, they can be overcome.