Mann, i've been wanting to go to london for years! I hope you have an awesome time!
Idk about sightseeing,but this warehouse place here, looks super rad with all the neon signs
Also camden marketplace looks like its got a bunch of interesting stores, check some out
Kyoto garden in holland park looks GORGEOUS
Take a photo of this oddity if you happen to be by billingsgate market
Covent garden, another shopping square
And these picnic spots if you're interested in parks
Hope you have fun!