Introduce irregular verbs
Irregular verbs require a special introduction. If students aren’t familiar with irregular verbs, they may find it difficult to form perfect tenses correctly. Irregular verbs do not have past and past participle forms ending in –ed. There are only a limited number of irregular verbs in English. Many of them are very common and hence it is necessary that you review them in your class and ask your students to memorize them.
Teaching the present perfect tense may be easier if you introduce the concept of finished and unfinished time. For example, yesterday refers to finished time. Today and tomorrow, on the other hand, refers to unfinished time.
Phrases that refer to finished time cannot be used with the present perfect. They need to be used with the simple past. Common examples are: last week, last year, in March, in 2011, in the 19th century etc. Phrases that refer to unfinished time can only be used with the present perfect. Examples are: today, tomorrow, this week, this year etc.
Make sure that students understand these differences and then give examples.
I met John yesterday. (Yesterday refers to finished time and hence we use the past simple.)
I haven’t met John today. (Today refers to unfinished time and hence it cannot be used with the past simple.)
I watched four films last week. This week I have watched only one film.
I had four cups of coffee yesterday.
Today I have had only one cup.
I read two books last month.
I have read all books in the Harry Potter series. (Here we use the present perfect tense because the reference is to an unspecified time in the past.)