Find what the sentences have in common. The sentences in a paragraph give details about one idea. For example, all the sentences might talk about dogs: "Dogs make great pets. You can run and play with them. You can teach them tricks. Dogs are always happy to see you."
Decide what the sentences say about the topic. A word like "dogs" is not a main idea. It is a topic, the subject of the reading. The main idea is what the writer says about the topic. In the example above, "Dogs make great pets" is the main idea because all other sentences provide specific examples of how it is true.
Look for a sentence with the main idea, or a topic sentence. Find a general statement that connects all the sentences. Don't choose a sentence that only gives details. For example, in this reading the main idea comes at the end: "Kittens are cute and furry. They look so funny when they get tangled in yarn. They curl up in your lap. Kittens are the best pets!"
If there is not a topic sentence, write one sentence that sums up the whole paragraph. Don't list all the details. Tell the message in a general way. For example, consider this reading: "Nicholas has a turtle. Sarah Jane thinks parakeets are interesting pets. Manny's favorite animal is horses." You might decide that the main idea is, "Everyone likes different animals."