Mazeltrick makes a very good point about keeping track of your own personal strengths and weaknesses. For instance, I know that I am deadly with Maiden Special Weight races and horrid on non-graded stakes. So, I tend to concentrate the majority of my funds on the types of races that I have shown the most consistent success. I keep a log of every bet I make and keep separate statistics on track, type of wager, and class of race.
When I'm playing Calder I play a lot of superfectas - this has been one of my most profitable long-term props. At smaller tracks such as Mountaineer and when I used to play Turf Paradise I concentrated on Win & Place bets because false favorites at such tracks often skew the odds more than at the larger tracks due to the small pools.
By no means do I have delusions that I could do this for a living -mostly due to the fact that I enjoy the "action" too much and do not have the discipline to wait for only the best of situations. But I can honestly say that I have not shown a loss for any single year since I started keeping detailed records in 1999. There were many years prior to that, however, when I was learning the game, that I donated regularly to the friendly teller.
I almost never bring more than $500 with me when I go to the track and when I play online I try to limit myself to $150-$250 a day max and if I get down more than $500 in any given week I will usually step back and take a few days off, maybe re-read some of my favorite handicapping books, or just take a break from horses all together.
I've had a couple of moments that have helped my bottom line including winning the Breeders Cup Classic superfecta for $12,000 when Tiznow stormed home. Hit a $5,400 superfecta on a $4 ticket at Turf Paradise and had the guts to bet $1000 of it on the Pats to win the Super Bowl at 10-1 before the infamous Oakland snow game. I almost never play pick 6's like many good players, but there are occasions when I'm feeling very confident where I'll play pick 3's and pick 4's. I've just found I have better success concentrating on one race at a time.
It's a game - and just like any other game it's entertainment. Hell, some guys spend hours reading the Wall Street Journal and lose their asses on stocks - I'd rather spend those hours buried in the Racing Form and win or lose I know I'm having a good time.