Knowing your Learners
Generally, it helps to learn more about how people learn. It also helps to understand human perception (sight, smell, taste, touch, hearing, and proprioception), particularly for accessibility design and pedagogical design. Finally, it helps to learn about "human factors" or about human capabilities and limitations.
Specifically, it helps to know about your specific learners, their knowledge levels, their cultures, and their learning needs.
Bloom's Taxonomy
Some use Bloom's Taxonomy to gauge the level of learning desired for the learning.
Bloom's Taxonomy of Learning / Bloom's Rose
(Note: The above is an open-source resource created by K. Aainsqatsi in 2008 and released to the public domain at http://upload.wikimedia.org/wikipedia/commons/2/24/Blooms_rose.svg.)
