As you've probably heard, Justin Timberlake reportedly popped the question to his on-again-off-again girlfriend Jessica Biel. Congratulations, you two! (Provided this report is real and not some false bit of fanfic and wishful thinking posing as journalism.) Hopefully the long-time couple are prepared for the ebbs and flows of married life, but -- if not -- they can look toward their own onscreen work as sources of inspiration for marital bliss. Ahead, six dos and don'ts the pair can learn from their movies.