Im what you call a "Straight Shooter". With all my tracking it's my aim to get the EXACT. Dont know if I could be of much help with "pairs" since we've never had that ability in Texas it isnt something that I have developed a method for tracking.
As far as Pick 3 in general, I would say first you need to learn the very basics of the possibilities of 10 digits 0-9. That being first there are exactly 1000 "exact" (straight) combinations starting with 000 and ending with 999. There are some very distinct characteristics of the 1000 exacts and the digits that make them up. For instance there are five Even digits (0-2-4-6-8) and five ODD (1-3-5-7-9). 75% of all the exacts will have either 2 Even digits with 1 Odd or 2 Odd digits with 1 Even.
There are 250 combinations that are PURES....meaning either all Even or all Odd digits. With 125 exacts in each there will be 5 Triples, 60-3 different digits and 60 Doubles. Of the 750 exacts that are 3-different digits, there will be 6 different "alpha patterns" such as EEO/OOE/EOE/OEO/OEE/EOO. Each of these alpha patterns will have 100 exacts each and 25 Doubles.
Another fact about the 1000 exacts is Sum Totals and the majority of the combinations will Sum 11-20 and will therefore play more often then Singles (0-10) and Twenties (21-27).
Another fact is there will be exactly 100 EXACT combinations with any specific digit in any given position of 1st, 2nd or 3rd. Fact, there will be a repeat digit from a previous days game about 60% of the time. I have seen this repeat rate drop as low as 50%, however, it doesnt stay there very long.
Knowing these "facts" enables you to filter out what probably will or will not play. Believing in these facts is another necessity. Then you can start keeping record of what does play to determine what is more likely to play then not. I use what I call a process of "elimination for determination".
If you can determine ONE digit that is going to play and what position it will play in you will reduce the 1000 EXACTS to 100. It takes more then this 1 method of reduction to reduce the number of exacts to where it is affordable to play though <G>