Here's what you need to do:
"To be in with a chance of winning, we want you to show us your photography skills using Black and White as your starting point – it could be a Black and White photo you've taken, or a colour photo with a Black and White theme (such as a chessboard or piano tiles, or as it's winter how about something in the snow?) the more creative and appealing the better."
After you shoot a photo, all that's required is to share it on Twitter with the hashtag #735style. The promotion is valid until midnight Monday 2nd February 2015, so make sure you get your entry in before the deadline. For all the legalese behind the promotion, head to the source link below.
Source: Lumia Conversations UK