The mayor has welcomed the lifting of the lockdown imposed on 5 November, saying that people can now start seeing more of their friends and loved ones while shops and hospitality venues will receive a major boost, Khan wrote on Twitter, where he also published a notice his office sent to all Londoners.
He stressed, however, that it is "absolutely vital" that people continue to follow the rules.
"If we act like this virus has gone away we could see a devastating further surge in cases at a time of year when our NHS [National Health Service] is already under enough pressure", Khan added.
Under the three-tiered system that replaced the national lockdown on Wednesday, non-essential shops and other businesses, including personal care services such as hairdressers and beauty salons, are allowed to open.
Under Tier 1 (medium), up to six people can meet indoors and outdoors, pubs, and restaurants are open until 23:00 GMT and spectators can attend sporting events in limited numbers.
Most parts of England, including London, will however, be in Tier 2 (high), meaning people are not allowed to mix with other households indoors, although they can socialise in groups of up to six outdoors, while pubs and restaurants can only serve alcohol as part of a substantial meal.
Other major cities such as Manchester, Birmingham, and Nottingham, as well as the county of Kent, will all fall into Tier 3, where people must also not mix with anyone outside their household or at most outdoor venues, and pubs and restaurants will have to remain closed except for deliveries and takeaways.