Running late for work, Steven notices and starts chasing down the double-decker bus that he's trying to catch. When he tries to get the driver's attention by waving frantically, he's using his right arm, but the scene then cuts to him now using his left arm and there is a travel mug in his right hand that wasn't there previously.
The couple that approaches Steven and asks him to take their photo as he is sitting talking to Crawley--the street performer painted in all gold--appears literally out of nowhere. Steven is mid-sentence when they show up to ask for the photo in one shot, but they are nowhere to be seen approaching Steven in the previous shot when he first begins that sentence.
After Layla hangs up on him, Steven dials the phone to try to call her back. This would only be possible if he had the number memorized, which he wouldn't. Cell phones store contact numbers and can be dialed or redialed with one or two button presses. There would be no need for Steven to type in the full phone number as he is depicted doing.
During Arthur Harrows ritual in the opening scene, he runs his finger across the rim of a drinking glass, producing a note. The glass is a common drinking glass called a Picardie, and is made from tempered glass, meaning it cannot produce a note.
In the restaurant scene, Steven calls his date, 1) he would have noticed his phone showed the day to be Sunday; 2) his date would have called him when he was late and left a message, which he would have gotten beforehand.
After his date goes wrong, Steven, a vegetarian, orders a steak. As he is unfamiliar with the steak-ordering process, the waiter suggests he get it prepared "well done." No employee of a high end steakhouse would ever suggest ordering a steak well done. Anything above medium-rare is considered overcooked and ruined. Some steakhouses will prepare a steak overcooked upon request but would never suggest it to a customer.