Winning Strategies
There are so many angles, i'm not going to list them all, you know which angles you like to use.

The key is figuring out when to use the correct angle, and the best way to do that is to look through previous races on the day and see which angle is hot at what particular track.

Another option is looking at which angle has the biggest advantage in a race, for example, if a trainer wins 20% of their races and every other trainer in the race wins less than 10% of their races then that is a big advantage and a positive angle play.

Here are a few angles i like to use that perform well:

Value Play: Take the 3 horses with the highest Beyer speed figure in their last or second last start and bet whichever one is at the highest odds.
This is a value play because you're getting overlay odds on a horse that might not be the best in the race but is close to it, and these horses will win more often than their odds suggest so it will turn out to be a positive play in the long run.

Extreme Longshot:
To find a big priced longshot winner you need to use an angle, the best ones are "hot jockey" and "track bias", a jockey who is riding good has a way of getting a horse to outrun their odds, and if a track is favoring closers or front runners you can find a longshot who can benefit from it, like the horse that goes to the lead at big odds to set the pace and carries their speed all the way because the track is favoring front runners that day. 
Other factors to look for are a horse's age, type of race, change of surface, equipment change, trainer preference.
Younger horses can improve quickly, you may see a young horse go from a claiming race to a stakes race and win at big odds because they improved between starts.
Some races produce more longshot winners than others, Maiden races crowded with 1st time starters and inexperienced horses have this reputation, (if betting 1st time starters look for a minimum of 9 workouts prior to the race), as well as big stakes races with a lot of money on the line, trainers will often point their horse to a big race and conserve them in recent starts, using them as preps, so the betting public may not get an accurate idea of the horse's true ability and overlook them.
A change of surface can bring a horse to life, a wet track, a deep track, running on the grass, a popular trainer move is running a dirt horse on the grass for a race and putting them back on the dirt, a horse that prefers the dirt will usually run better after a move like this.
Equipment changes and addition of medication can really help a horse that's been having problems, addition of Blinkers or Lasix are usually positive moves.
Trainer preference means that some trainer's have a reputation for doing things well, like stretching out a horse to run from sprint to distance races, getting a horse to run well first time out or after a long layoff, producing quality grass runners or sprinters, etc, trainer Bob Baffert was a champion Quarter Horse trainer with a reputation of being able to get horses to run fast, as a Thoroughbred trainer he's produced several Breeders Cup Sprint winners and big running longshots that almost won.

Competition:
During a meet you will often find jockeys or trainers that are competing for the riding or training title, especially late in the meet, if you see the top 2 jockeys or trainers are close in wins it's a good idea to put your money on them.

Reunions:
A jockey reuniting with a horse that they have had success with in the past, or a jockey riding for a trainer that they have success with, (25% + win), is a good betting angle, look for both those angles on the same horse.

Jockey/Trainer Combos: Look for consistency when using this angle, 20% Win, 50% ITM, and 2.00+ ROI with a minimum of 20 starts together are a good indication of a succesful and profitable tandem.

Condition Jockeys or Trainers: Some excel in particular race conditions, sprints, turf, etc, pay attention to these types, they usually bring home decent priced winners.

Class: A horse dropping down in class is always a threat, provided they ran respectably in their previous race, for example, a horse dropping down from $20 000 to $10 000 that got beat less than 10 lengths is a better bet than a horse dropping down from $50 000 to $10 000 that got beat by 20+ lengths.

Combination angles normally work best, that is when your horse has more than one factor in it's favor, a hot jockey/trainer combo combined with a class dropper is an example of a favorable combination angle, using combination angles with jockey/trainer stats and ignoring a horse's form is also a good way of hitting a big priced longshot winner.

Strategy Books
WINNING TECHNIQUES is available free for download and recommended reading, you can also read a chapter from Bet With The Best: Expert Strategies from America's Leading Handicappers.
 
 
Other popular books are listed below and available for purchase on Amazon.com

DRF WinningTechniques

Winning Techniques
The paper to read when you're playing to win
 

Racebooks

Racing

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