A few tips I suggest you take on board. I learnt these from experience...so for your own good, learn from my mistakes!
1.) As glam as you'd like to look for a day touring round London, Stiletto heels are a massive no-no. Unless you'd like to be hobbling down Regent Street bare foot and bleeding, i'd recommend you stick to comfortable foot wear. A pair of grungy boots are just perf for a visit to Brick Lane.
2.) As exciting as Camden Market is, don't get to hyped up on the hysteria of the place, or you'll find yourself causing your mind and body serious damage. For example, do NOT be charmed into a "hairdresser" free of charge by a gorgeous, blue eyed guy called Levi. Turns out, the hairdressers there weren't qualified. Oh well...at least hair grows.
3.) As creepy as the tubes are at night time thanks to the horror movie 'Creep', i recommend you DONT get a taxi instead. They tend to choose the longest route possible, add major congestion charges and therefore result in your purse being emptied. So say good-bye to that top you intended on going back and buying, unless your willing to to sit through the 3 minutes of eery loneliness on the tube platform.
4.) Admittedly, London can be a bit pricey, but as opposed to tiny towns with just a few highstreet shops, there are thousands of tiny boutiques and vintage shops. Perfect for those of us who prefer to be original. Also you'll find Brick Lane and Camden Market has plenty of interesting original pieces.
5.) If your visiting from abroad, you couldn't possible leave without the infamous 'I <3 London' Souvenirs. Lucky for you there are hundreds of little souvenir shops full of t-shirts, hoodies, shot glasses, even condoms. But like any store like these, you'll find the salespeople are probably willing to lower their prices slightly. So don't be a pushover, hold your ground and leave that shop with one hell of a bargain!