Getting lost is an age old suggestion but a good one. Put away your cell phone or your A-Z and just wander around. I still do this regularly even though Ive lived here for nearly 10 years. London is a big city and it drip feeds you its secrets sometimes. You will come across things you wouldn't usually, in amongst the Starbucks and pret a mange there are some amazing sights. Just 'being' somewhere is a great experience and one no guide book can help you find.
This beautiful 19thC industrial building is situated in Markfield Park just around the corner from my studio. Once a sewage treatment works serving the whole of Tottenham and now a museum. The fully restored Victorian pump engine is only open to the public on the second Sunday of every month but the outside of the building and surrounding park is a worth a visit regardless.
Donlon Books is an atmospheric little bookstore on Broadway Market (in East London.) They sell rare art books, style publications, and homemade photography zines.