I would recomend somthing very simple to start until you understand and have studied some other ideas...

1) add together the beaten lengths of the last 3 runs
2) add to this the price in the morning paper

thats it for now...here is example
Last start 2nd 2.1 lengths
2nd last start won =0
3rd last start 4th 1.5 lengths
price 4/1

2.1+0+1.5=3.6
4/1 in dollar amount is $5 so that makes it 5
3.6+5=8.6

do this for all runners then back the top ranked runner