M. David Merrill reviewed instructional design theories to identify common principles.  He devised the following five principles.

1. Learning is promoted when learners are engaged in solving real-world problems.
2. Learning is promoted when existing knowledge is activated as a foundation for new knowledge.
3. Learning is promoted when new knowledge is demonstrated to the learner.
4. Learning is promoted when new knowledge is applied by the learner.
5. Learning is promoted when new knowledge is integrated into the learner’s world.

First Principles of Instruction by M. David Merrill

The American Psychological Association has developed the Learner-centered Principles. The most important principle is to create a positive climate and positive relationships.