To find the main idea of a piece of writing, you can employ the techniques in which you?

The main idea in a given piece of reading is implied by the introductory paragraph, and, or several meaning sentences that are in subsequent paragraphs.

Explanation:

The main ideas in the a given piece of work, specifically reading is contained in the first paragraph of the piece of writing. The first paragraph can be used to imply the main ideas in a topic without necessarily revealing it. The first concepts, terms, illusion and characters mentioned, certainly we can deduce the main idea.

Several sentences in paragraphs that carry almost similar, related and interrelated facts, in most cases are very essential in explaining the main idea.  By looking at them in various paragraphs, one is able to find the sole message being communicated.

the wires in the toaster turning red and the toast crisping and turning brown