Wardy gives some advice on how to improve your schematic and PCB design skills. His advice is to clone consumer products with available schematics. He provides links to a few examples to get you started.
Using a realistic design will confront you with the kind of obstacles that present themselves to the original designers themselves (things like searching for footprints that aren’t in your parts library) and also the more tangible mental exercises such as trying to cram 250 parts (and the many hundreds of traces that interlink them) into 20 square inches of circuit board!
For a less adventurous approach we recommend removing some or all of the traces from the PCB on your favorite open source project, then re-routing them.