I live in London, so i can drop you any info if you decide to come over here.
To be honest, as someone who lives here, unless you have enough friends going with you or you're going with a partner, or enough contacts over here, London would probably be a pretty bewildering place, as well as to know the good/bad/ugly parts to go to. Depends what you want to do , though saying that, you can do pretty much anything.
Paris - sick. I prefer to London. More relaxing, nicer architecture...yeah just sweet.
Berlin - also rad. Although as someone said, you need to have contacts or at least know what you're doing or you get pretty lost and depressed. Some amazing bars/clubs though - check out Studio 54 in the abandoned squat building thing if you get a chance, if you're a writer also a bonus.
Amsterdam - drugs and sex. And the Rembrandt and Contemporary Art galleries. Apart from that, don't bother, unless you want to have sex with 54 year old post-op trannies and smoke alot of fine thai.
Prague - totally amazing, go. Getting very popular, but massive student scene, wicked nightlife..just yeah, good. Also a good hip hop festival every year called Hip Hop Kemp.
Rome - overrated. Good food though. If you're going to go to Italy, go somewhere outside one of the cities, a small town, like Siena or somewhere.
Those are usually the main tourist spots in Europe, but I've been to a load of other places so if you're planning to go anywhere else, shoot.
On that note, I'm going to New York in the summer, but on the family holiday tip. As i'm a bit of a hat/trainer fanatic i was hoping someone could drop me a few places to look up? was also planning to get to Supreme if i could...
no art fag comments please, ha..