The problem that many horse racing handicappers face is that they don't have much money. Making a $2 win bet on most winners isn't going to return much. On the other hand, it you make a $1 key bet and play that winner over two other horses, you could win the dollar trifecta and that could pay a lot. It will certainly pay much more than the win payoff.
The problem of course, is to limit the number of combinations to keep the cost of your trifecta key bet down to a minimum. You need a strong key horse that will have a high percentage of winning. Therefore, the way to find a good key horse, if you plan on putting it on top of your tri key bet, is to look for a horse that has a clear statistical advantage over the rest of the horses.
Though it is common knowledge that favorites win about a third of the time, here is a little known fact. There are some races where favorites win more than a third of the time and other kinds of races where they win a lot less than a third of the time. For instance, in certain races favorites win more than half the time. Just by keying on the favorite over two other horses, you have a key horse that will win more than it loses. You can find these statistics from some of the major suppliers of past performances who now print the percentage of winning favorites for each race, based on the conditions, at the top of the program.
Just find a race where the favorite wins a high percentage of the time and you have your key horse. With a little practice you'll get good at spotting which horse is going to be the favorite, it is usually one of the two top horses in the morning line.
The next step is to find good horses to place after that favorite. I recommend you look at the percentage of place and shows to the actual number of races a horse has run and use several of the horses who run 'in the money,' very often. Just add the place and show figures for each horse and then divide that number by the total number of races. You will then have a key horse that will win a high percentage of races and your other picks will also be horses who run in the money very often.
This method may not make you a fortune, so don't mortgage the farm, but it should hit a high percentage of trifectas because statistics will be in your favor.