Here in South London, no matter how dodgy the local park is, you can be sure to see numerous people running in it (especially early in the week, on warm nights). For Clapham and Brixton - Running is the New Brown.
The great thing about running is that it's a pretty inclusive sport. Here's how you can take part:
1) Buy as much varied running clothing as you can. If you're a boy, buy some dark shorts and a handful of sport t-shirts (Nike, Reebok, etc). If you're a girl, either buy everything in white, or buy some black shorts and some bright t-shirts. If you're slim, then skin tight clothing is de rigeure.
2) Shoes. These are pretty important, but don't go wasting your money at Runners Need or the Marathon Store. Buy the most fasionable trainers you can. Ideally colour co-ordinate with your clothing (so you may need more than one pair). Make sure you've got some of those trainer socks (or ordinary white socks, which you must pull up if you're a bloke).
3) Under no circumstances should you ever attempt to run when it's cold, wet or generally unpleasant. If it's dark, you may want to avoid running, because of course, less people will see you.
4) Run on a Monday. Monday's the least likely day for socialising, so keeping fit needn't interfere with heavy drinking. If you're still struggling from the weekend, then Tuesday is acceptable, but be warned, the opportunity for posing is much reduced.
5) Generally speaking, listening to music is advisable (unless you're running with others). If you are listening to music, you simply have to have an iPod. Generic MP3 players are deader than a-line flares with pockets at the knees.
6) Choose your running partner carefully (if indeed you're not running solo). You do need someone of similar ability, but they also must be of the opposite sex. Group running is okay, and of course gets around any gender issues (and leaves a little more room for a range of ability).
7) Don't run enough to break a sweat. Sweating is incredibly unattractive, and really doesn't make you look "hard". Make sure you carry a water bottle to rehydrate in the sun. Generally speaking, Camelbaks are a bit too serious, and make you look like you may sweat soon.
8) Look at your fellow runners, but don't 'check them out'. Even though you're out posing, don't let on that you're also checking out the menu. If it's sunny, then letching glasses are advisable.
9) If you need a rest, push a tree. Tests show this is by far the best way to look like you've actually been doing some exercise, even if you haven't.