I've complied some information here that may be relevant to planning your trip. It contains links to aid your in preparing to have the best possible experience on your visit to London. I make every effort to keep it up-to-date but be aware that specifics may change on short notice.
There are the topics that I get asked about most frequently, so to make it easier I've complied all the information here in the form of a handy guide.
Paying for public transport
You can use a contactless card (a credit card that you pay with by tapping on the payment device), Apple Pay, an Oyster card (stored value card), or a Travelcard (paper pass) to pay for travel on the Underground (tube), buses, trams, the Overground, and some boats as well. This function may need to be activated before you can use it and some cards from other countries may not work. Each person 11 and older (children 10 and under are free and 11-15 year-olds pay half price) needs to have their own card; it is not possible to pay for multiple individuals with single card and you cannot pay cash on buses either. The prices are the same whether you pay with an Oyster or credit card. You can find all the specifics you could ever wish for here:https://tfl.gov.uk/fares/
London is a largely cashless society. You may find a few small restaurants that only take cash but that is rare. Even the buskers playing music in the tube and markets vendors have mobile credit card devices and you can use contactless payments for amounts up to £100.
Despite sensational headlines, London is generally safe in most of the major areas that you will frequent. People are generally friendly and helpful and will assist you if you need it. You can also approach the police for directions or advice.
There are a few things that you should be aware of when traveling around London on foot. The most obvious is the necessity to be aware that the traffic may be coming from the opposite direction than that which you are used to, so you need to look right, left, right instead of left, right, left as you would in the US and European countries. The fact that this is painted on the road surface at many intersections is a helpful reminder.
Electric cars also present a danger as their lack of motor noise means many don't realise they are there until it's too late. Also, the narrowness of many streets and pavements (sidewalks), coupled with large crowds, results in you often being a lot closer to moving vehicles than you may be accustomed to in your home country. Resist the reflex to step into the road to avoid oncoming pedestrians.
A chronic habit of Londoners to cross against the red lights at intersections (and in the middle of the road) presents a danger to visitors who may follow them without looking to see if vehicles are approaching. The locals know the order of the lights but visitors don't and so are more in danger. Always be aware of your surroundings and don't step into a roadway unless you have checked and are safe in the knowledge that there are no vehicles approaching. And don't blindly follow others!
Keeping your belongings safe
It's important to always be aware of your things. Always have a specific place in your bag or wallet for items so you will know immediately if they are not there. Get in the habit of looking back at the tube or bus seat you just stood up from before exiting to check that you haven't left anything behind. Don't keep valuables in outside pockets of backpacks and carry your backpack in front of you in crowded areas where people may gain access to it. Avoid holding your phone too far out from your body on tube platforms or on the street as someone ma snatch it and run off. A good idea is to have a foldable tote bag in your purse or backpack that you can use to keep things that you pick up or buy together.