Observe and identify designs around you.

Keep a Design Notebook to note down the designs you observe and like.
Do the same for flawed designs or designs you don’t like. Before you even realize, you’ll find yourself looking and understanding designs with greater acuity.

Read Design magazines.
Metropolis, iD, O Magazine, and Dwell are a few examples.

Visit a Design Museum.
Consume not just things, but the experience of witnessing them.