I think it would be good idea to prepare 2 short texts for the students. The 2 texts should cover the same topics, choose a topic that is usually written in the present simple: e.g. people’s daily routines, habits, likes and dislikes. One should be written using “I” the other should have “she” as the subject. Choose or write texts with vocabulary that the students understand. Have the students read or listen to the texts and give them some questions to answer to check they understand.
Then focus on the language used. Put some sentences from each text on the board and point out the differences in the sentences. Ask students to tell you why some verbs have an “s” and others don’t. They can do this in their own language if they don’t know enough English. Remember to point out that some verbs take “es” in the 3rd person singular. You can then do some controlled practice of the structures, for example sentences with gaps to fill in.
You can follow this up by asking students to write a few sentences about themselves in the present simple using “I”. Go around the class and make sure the sentences are correct. Students can then get up and move around the classroom. They say their sentences to their classmates (or read them out, if they don’t remember them). While they are circulating, they can make a few brief notes about the others in the class. Students then write what they remember about the others (e.g. John takes the bus to work; Jane watches TV every night); it’s a good idea to do this in pairs.
I hope you and your students will find this useful.