Plan your holiday
As we have said before, in your research you will find places you wish to visit. If they need tickets and you can buy them in advance and on-line, then do so. It avoids disappointment. It gives structure to your holiday. It convinces immigration you are here for legitimate purposes. It can save money, perhaps including fees.
Trans especially are so much cheaper in advance. Many sites like Trainline do clever split tickets that save a bit. Look to travel at off-peak times. Look for family tickets and offers.
For special exhibitions or popular sites, they sell out quickly. Even free entry places like Sky Garden require a ticket in advance.
Making an effort to go somewhere then finding no tickets on the day is very disappointing.
And buying in advance, before you leave, spreads the cost and softens the impact of the bills somewhat. Even buying in advance when you are here is good.
At the airport
When you arrive, be sure you know how to get to your final destination. Look at the advice we have given. Avoid at all costs random people hanging round the arrivals touting for business. Who knows who they are and if they are safe? Who knows what they will really charge?