Patterns are especially useful for sparking ideas. Copyright free art is great fodder for sparking ideas or practicing your lines. A focus on pattern and design... all images are copyright free from the New York Public Library Digital Gallery.
a. Doodling. Doodlers are always looking for pattern inspiration. Take a pattern that you find, break it apart, re-arrange, invert, skew, play.
b. Sketching. Add patterns to your sketches in spots where it is logical to have a pattern, but there is none in your source material. Good spots include dresses, scarves, towells, framed art, bed spreads, wallpaper, carpets, flooring, table cloths, pots, ceramics, tea cups, curtains.
c. Line Practice. Absolutely fantastic fodder for drawing better lines. Practice curves, lines at certain angles, drawing without turning the page, parallel lines, symmetrical shapes. A great way to practice productively is to draw a border or frame around your art, doodles, art journal pages, etc. using a pattern you have developed.