Provide a Cancel button if it adds clarity. A Cancel button instills confidence when the user is abandoning a task. Cancel buttons should always be included in action sheets at the bottom of the screen.

Make destructive choices prominent. Use red for buttons that perform destructive or dangerous actions, and display these buttons at the top of an action sheet.

Avoid enabling scrolling in an action sheet. If an action sheet has too many options, people must scroll to see all of the choices. Scrolling requires extra time to make a choice and is hard to do without inadvertently tapping a button.

Use verbs in titles. An action-specific title shows that a button is interactive and says what happens when you tap it.

Use title-case for titles. Capitalize every word except articles, coordinating conjunctions, and prepositions of four or fewer letters.

Keep titles short. Overly long text can crowd your interface and may get truncated on smaller screens.

Consider adding a border or a background only when necessary. By default, a system button has no border or background. In some content areas, however, a border or background is necessary to denote interactivity. In the Phone app, bordered number keys reinforce the traditional model of making a call, and the background of the Call button provides an eye-catching target that’s easy to hit.

Use Detail Disclosure buttons appropriately in tables. When a Detail Disclosure button is present in a table row, tapping the button shows additional information. Tapping elsewhere selects the row or results in app-defined behavior. If you want people to tap the entire row to see additional detail, don’t use a Detail Disclosure button. Instead, use a disclosure indicator accessory control. 

Allow keyboard entry in addition to the Add Contact button. The Add Contact button provides an alternative, not a replacement, to typing contact information. It’s fine to provide it as a shortcut for adding existing contacts, but let people enter contact information with the keyboard too.