Getting students to write out a dialogue and having the teacher correct it before practicing it out loud is a good way to practice sentence structure. By having students talk about what they did last weekend, they will be using the past tenses of verbs, as well as nouns, they would use in a real conversation. This can be done in classes of all levels, in groups of two or three. Get the students to use as many different verbs as possible in a conversation they would really have with a friend. Have them both ask and answer relevant questions.
In pairs, have one student try to persuade the other to do something, like go to a concert or on a vacation with them. The one trying to persuade the other can list many reasons why the other should agree. If he is trying to persuade the other to go to Madrid, he can tell him about the attractions, food and history, while the other has to make excuses for why he does not want to go.
What If? exercises are fun because they allow students to use their imagination, be a little silly and use the conditional mode of verbs, which is not as easy as the English conditional. Actors in this dialogue could be friends, a parent and student or a teacher and student. The dialogue could start off by one asking the other what he would do if he found a million dollars. The other would reply using the conditional mode. He could then ask the same question or a different one, but also in the conditional. The dialogue could also start by one asking the other what she wants to be when she grows up.
Put the students in groups of two. Have one student choose a celebrity or hero of his that he would like to be--for example, a rock, sport or movie star. The other student will be the interviewer. The interviewer will ask relevant questions about the other's career, life, past and future. This is a good exercise for having the students use their imagination and many different tenses: the present, to describe things they do each day; the two past tenses; both forms of the future; and the continuous present.
Restaurant dialogues are a good way for students to familiarize themselves with food and drink names. Have students get into groups of three, two customers and one server. The server tells the customers about food specials and the customers ask questions about the food. After ordering, the customers can talk about which foods they like. When the food comes, one of the customers is not happy and wants to return her food. She has to tell the waiter what the problem is.