I love mixing it up with pattern. The key to mixing pattern is all about scale. The large windowpane check fabric on the chair mixes well with the slightly smaller scale drapery print, while the neutral ground on the walls binds everything together. Don't be afraid to mix up patterns; its all about the scale, proportion and balance. Pick the most dominant color from the patterns to tie everything together. In this story, a pillow in the same fabric as the draperies would be a nice addition on the chair.