Here are my top recommendations for Hotels in London based off places I've stayed or places I would like to stay in the future! I always like to book my hotels and accommodations as early as possible because I find the rates are usually better well in advance (meaning 6+ months out) and then I can book and forget about it until closer to the departure date. I also always book places with free cancellation in case my plans change or I find a better place elsewhere or last minute. Free Wi-Fi is a must for me and location is key. I typically start with a landmark or neighborhood I want to stay around and then compare hotels in that area.
If you're looking for a larger space or a more local experience, check out Air BNB, Wimdu, or Home Away for apartment and home rentals. If you're backpacking or looking for a free or cheap place to stay, check out Hostel World or Couch Surfing.