When to go
Piccadilly Circus can be visited year round, but you'll need to go to this location during, or after, heavy rainfall to photograph a similar reflection of the building in the street.
August and September have the heaviest amount of rainfall, so I recommend visiting then if you can. Also, by that time of year, the sun will set earlier, so you'll be able to arrive at a reasonable hour and have plenty of time to shoot.
At night, the city lights (especially from the big screen behind you) will provide the most contrast against the dark nighttime sky.
If you take this photo earlier in the evening, you won't be able to see the rain in the air.
Field tips
I used a very wide lens (14mm) so I could capture the full reflection of the building in the street.
A tripod is essential to get the motion of the red buses and the rain. Experimenting with different exposure lengths will allow you to see what works to get a familiar shot.
If you have a tripod where you can mount your camera upside down, it'll mean you can get very close to the surface of the puddle, which will give you the clearest reflection.
Current weather
Do nearby
Regent Street is filled with great photographic opportunities — especially with its symmetrical design. There are leading lines everywhere you turn, making for some interesting perspectives.
If you enjoy shopping, you'll discover that this area has some of the best high-end shopping in London.
For food, I recommend visiting the nearby Soho district because you can eat almost any type of cuisine you desire.
You can also wander down to Chinatown in about 5 minutes if you'd like to have a taste of some authentic Chinese dishes.