Better sentence-writing in 30 minutes a day - Dianna Campbell 1995

The irregular verbs
-Ed endings
Revising at the word level

The irregular verbs are not as easy to form as those that end in -d or -ed. To learn these, you have to memorize them. Here is a list of the most frequently used irregular verbs. Underline the verb forms that sound unfamiliar to you; then practice them in your writing as often as you can. We’re using have as the helping verb here, but you know that other helping verbs are used as well.