Race odds are actually percentages not dollars [$3.50] or fractions [5/1].
Your market is the winning % chance of your top 3 to 5 horses [depending on race size] in a race.
All horses combined in a race equal 100% total chance [don't get this confused with bookie or TAB !00%+ markets even if your on the gold coast facing a 200% bookie market]. We are talking about actual winning chance.

As a rule of thumb, in an average twelve horse race for your top five runners you should set your market to 80%. The other 20% represents the rest of the fields chances combined.
For smaller fields of 4 to 7 can be about 90% for 7 runners and about 95% for 4 or 5 runners.
Large fields of 15/18 should be anywhere down to 60/70%.

All you need to do to frame your own market is to turn your opinion of each horse into a number between 1 and 10.

A really big chance [Makybe Diva] or any real stand out would be a 10
An an outside chance 1/3,. some chance 4/6, a good chance 7/8. Anyway you get the drift.
Practice will make perfect and it becomes very simple once the concept and how it works quickly falls into place [from actual practice].

For our 5 runners in this imaginary 12 horse race we'll set the market to 80%.[ 5% either way is not critical].
We have looked at the form and decided there were 2 really good about equal chances and another 3 with some chances.
We have scored them: A =8, B =8, C =6, D =5, E =3. Total number of points = 30.

We now divide each Horse's point number by their total. 30 in this example and multiply by our 80% market.
Eg: divide 8 by 30 and multiply by 0.8 [80%] and we get 21.333332 [8/30 x 0.8 = 21.3%]

The winning % chance of each horse in our opinion has become:
Horse.....Points.......Calculation...... Winning Chance
A................8..............8/30 x 0.8.........= 21.3%
B............ ...8..............8/30 x 0.8.........= 21.3%
C................6..............6/30 x 0.8.........= 16%
D................5..............5/30 x 0.8.........= 13%
E................3..............2/30 x 0.8.........= 5%

To calculate the price for each horse, divide its winning % chance into 100.
Eg: [A] 100 divided by 21.3 = 4.69 or $4.70

We are now armed with our own prices based on our opinion, not someone else's.
A. $4.70, B. $4.70, C $ $6.30, D $ 20

We look at the prices offered and we find: A $5.50, B $7, C $3.50, D $16
We have an obvious [to us] false favorite C. Our bet would be to take both A and B or probably B straight out as the best value.
Ignore your personal fancy.

If your having a straight out bet go for the better value of your top 2 as you are wrong more than 75% of the time [mostly] anyway. If C was $15 there is a good bet in taking B and C to win or even just C.

Do all this 500 times and you will be making money if you have spent a bit of effort in learning how too handicap a race and then do your own priceline on the top 3 to 5 in the morning market. It's value we are looking for not your winning preference. The public are wrong 70% of the time, represented as the fav. and they can select the winner better than we can. We need VALUE, not a selection we think will win at any old price.

Follow your preferences/selections regardless of price and you will be making donations to TAB shareholders and Bookies for the rest of your punting life.