If your device is running Android 4.2 or later (until 5.0), you can add a widget to your lock screen using the following steps:

1. From your lock screen, swipe to reach the leftmost lock screen page.
2. Tap on the + icon to add a new widget.
3. Tap on the Remember The Milk widget. (If you're not able to select a widget, it may be necessary to unlock the device first.)
4. Select the view you'd like it to show and tap Save.

If your device is running Android 5.0 or later, lock screen widgets were replaced by Android notifications and the ability to swipe directly to your camera or phone.