Winning professional gamblers make money as they bet at value odds. They probably either have inside information or own superb horse racing systems to work out the odds better than bookmakers.
The most direct way to search for value is first to establish the true odds of the event happening, then seeing if and how they differ from the actual bookies odds available.
Bookmakers do not make many mistakes with their odds but they still can be beaten. For example a few years ago two punters traveled the whole country visiting independent bookmakers to get odds about a Hole in One happening in a particular golf tournament. They had estimated the true odds to be about 2/1 that someone would score a hole-in-one in a given tournament. But they managed to take prices ranging from 16/1 to 100/1 from many different bookmakers.
These bookies did not do their homework and thought that a hole-in-one rarely happened, and taking any bets was like money in the bank to them. These two gamblers made thousands of pounds simply by getting fantastic value on an event that, for once, the bookmakers priced up wrongly
Somehow you have to work out in your own mind the price you consider is a true one about any horse you wish to back.
Using Ratings, be it form or speed based, can be good tools in assessing Betting Value
A genuine value punter is typically unconcerned about backing a horse other than the favorites. The favorite is more often than not the horse with the best chance of winning, but the value in the race is often in backing horses more likely to lose. Backing horses with a price that suggests a 10% chance of winning, ie 9/1 when the true chance is 20% and 4/1 makes sense. They will not always win, but they will win enough times at generous prices and you will collect more money than you stake.
This is a very simple strategy to obtain value. Look for false favorites in horse racing. They may be favorite because they won their last race but check to see if it was in a lower class. Or they may be favorite just because a top jockey is riding it but you may have found a horse with a better chance going on form study. Opposing the favorite means fewer winners but you will win enough times at bigger prices to see you collect more money than you stake.