Two types of grammatical errors that nonnative speakers of English tend to make are:
English can be hard to learn as a second language, specially when it comes to learning irregular verb forms for all tenses. For example, the verb drink changes in all tenses: drank (past simple) and drunk (past participle).
As a consequence, nonnative speakers tend to use the simplest form of the verb, as in: Yesterday I drink orange juice for breakfast*. Here, drink was used instead of drank, which is the correct form of the verb for the past simple tense.
   2. Omision of an article
Since virtually every rule for the use of articles in English has many exceptions or subrules, and  the interactions that occur when two or more rules apply can be very difficult to  predict, nonnative also tend to omit articles a/an or the as in I threw ball* . Here, for instance, it is important to learn about countability, that is, if the noun phrase following the article is countable or not. Ball is the noun phrase in the given example and it is strongly countable in this context. Therefore, the correct use would be I threw the ball.
