Here are some tips for finding a room in London. This is based my personal experience to find a room through SpareRoom.co.uk and your mileage may vary. Some things to keep in mind is that I moved in September, a busy time of the year, and that I didn't have connections or friends to speed up the process.
Get lucky or lower your expectations: The room that you want is certainly out there but whether you'll get it is a different story. I've found and replied to rooms that looked perfect in terms of commute time, location, flatmates, the whole shebang. But alas, I didn't get those room for a variety of reasons, most likely because someone else was chosen.
Call instead of email: This is the only way to get noticed. My first approach was to send loads of emails to all rooms that looked interesting but that didn't work. I've learned that rooms in London are in high demand and tenants are frequently found for a room in a matter of hours or days. That means people take a room without viewing it (do they?) or their approach is different from mine. I can see why that is sometimes a decent approach (e.g., far away from the UK and unable to view it) but I'm currently in London so I'd rather view the room and meet the flatmates first.
Spend some time on the message you send: If you do send an email make sure you spend some additional time to craft the message. I'm not necessarily talking about grammar and punctuation (but do check that too). I'm more talking about the fact that you now only have one shot to convince the current flatmates to get back to you.
Even if you call they may ask you to send a message which allows them to sift through the interested people and find the ones that they would possibly want as flatmate. I would do that too if I were looking for a flatmate but it stacks the odds against potential tenants as they know more about me than I do about them. Most ads generally don't have much info about the current flatmates so you're running blind in that respect.
When you've found a room that belongs to an agency then it's easier as you're not directly talking to the flatmates. The agency wants to make money so they're more likely to arrange a viewing.
What can also happen is that current flatmates have run out of time in their personal agenda to make viewings possible. You may have called quickly once the ad appeared (or so you thought) but they're way too busy already with scheduled viewings. Better luck next time.
More search tips when looking for a room
Usually when looking at an ad you're looking for the basic criteria (location, price) but you're also looking for potential red flags that (should) make you reconsider.
You're looking for something (e.g., a good landlord) but you only have limited information. A great landlord may write a room ad in ALL CAPS and crappy English but it's more likely that he/she would spend some more time on crafting a decent ad.
Some other tips:
Don't necessarily restrict your search by checking all the boxes. I initially had "sharing with professionals" ticked but that also excludes flats where that information of other flatmates has not been filled in or where the flat is half students, half professionals.
Try not to confuse the price per week with the price per month. You can't simply multiply the price of a week by four and expect that to be the price per month. To obtain the price per month, you need to compute: (price per week * 52) / 12. As there are 12 months in a year, you can't multiply the price per week by four because that would lead to 4 * 12 = 48 weeks and not 52 as usual (in most years).
Why London is considered expensive
On a fun note, you sometimes encounter rooms that are outright bizarre. Just to give you an idea of how expensive London is, I've included the following photo. For 80 pounds (inclusive) a week you can call yourself the proud tenant of the following room:
That's right: you'll be sharing a television on a fridge with three others, all in one room. When the number of flatmates significantly starts to exceed the number of rooms, you know it's time to mark the room as unsuitable and search for another one.
For this room, the price a month of 320 pounds comes to about 400 euros at the time of writing which goes to show that London is a whole different world compared to student rooms in, e.g., Amsterdam and Utrecht, or even the accommodation that I stayed in in Melbourne, Australia.
In the end everything worked out just fine. This blog post has been in the pipeline for about three months now but I didn't get around to publish it until now. When I moved to London I spent about seven weeks in hostels before finding the place where I'm living now.
Arriving in London in September when many international students are also looking for a place to stay isn't exactly ideal but it also means there are a lot more properties on the market for renting.