C - Contrast. Elements that aren’t the same should be very different so they stand out. You do not want a sea of boring.
A - Alignment. Everything on the page needs to be visually connected to something else.
R - Repetition. Repeat styles to make the image seem intentional and thoughtful.
P - Proximity. Proximity creates connections. If things are related, they should be closer together than elements that are not related.
E - Edu Connections. A really creative image not connected to the learning objective will not earn you credit.
There are many choices out there, you are not just limited to the recommended apps.
Six Word Story
Tell a story with 6 words.
Not five, not seven, exactly six.
Post your finished images on Edmodo.
There are many examples out there, including a Flickr group with plain images and 6 word captions.
Three great examples (besides Ms. Butler's to the left):