This link is to the ACT writing page. If you follow the RUBRIC, you will be successful.
This link is to the ACT site on which the essays are graded and explained.
This link is to an older site. However, the ACT has shifted back to the old grade standards so it is not bad.
This link has some great inside hints. Please note the one on attention to actual details.
This link is to Peterson's ACT materials.
This link is to great video series on the writing portion.