For my part, most of the speculation I do is through part-time sports betting and trading. Even though I could probably go full-time, I simply don't think that I could deal with the stress of having my entire means coming from gambling! I only ever bet on sports that I can watch live and usually keep it down to tennis, soccer and Gaelic games. My tactic for betting is based on the completely unscientific method of gut-instinct and hunches! I know it sounds ridiculous, but I can often look at an odds market and know instinctively that it's just completely wrong.
My primary tennis tactic is finding a highly talented youngster, following him relentlessly and trading on the in-play volatility. Andy Murray was a goldmine for me in 2007 and 2008. Three times I was able to back him at prices of around 100/1 when he then went on to win his match. Of course, I was wrong more often than not with Andy, but when you're dealing with odds of 100/1, you only have to be right 1 time in 100 and you're set. Juan Martin del Potro was doing a great job for me this year until he came back he came back from 100/1 to defeat Nadal in one tournament (guess who got on that trade Now that del Potro has kind of established himself, I'm currently looking for a new up and comer!
Don't get me wrong here though. I'm not just blowing smoke up my own ass and trying to claim that gambling is easy. Even on a highly liquid betting exchange with a small operator cut, over 95% of punters will make losses. The obvious key to winning is to make more money than you lose. However, even if you have some sort of edge that ekks out a profit, you need cast-iron discipline. That means that you work with a bank of X and you commit to a maximum bet of YY% of that. Personally, I restrict my self to betting on one event a day (although if I spot a bet I simply can't resist and I'm in profit for a day, I'll allow myself an extra event of trading). I keep detailed spreadsheets of all my trades and have Excel spreadsheets done up so I can gauge my performance and to adjust tact.
I sometimes read the betfair forums, but it's almost impossible to pick out the few crumbs of wisdom from the rubbish. Would definitely be interested in getting in touch with other sports bettors/traders who know what they're doing.