What cultural faux pas should I try to avoid making in Lille?

"When visiting Lille, avoid speaking loudly in public places, as the French tend to value discretion and may find it disrespectful. Make an effort to speak some basic French phrases, as locals appreciate when visitors try to communicate in their language. Do not expect shops and businesses to be open on Sundays, as many close for the day. Avoid discussing personal income or asking about someone's salary, as it is considered impolite. When dining out, do not ask for substitutions or changes to the menu items, as French cuisine is highly regarded and chefs may take offense. Remember to greet shopkeepers and service staff with a polite "Bonjour" upon entering and "Au revoir" when leaving. Finally, be aware that the French tend to dress more formally than in some other countries, so avoid wearing overly casual clothing, especially in upscale establishments," said another expat in Lille, France.