I see a lot of people who don't train their pets and have spoken to some who just don't understand pet training so they are holding off on it for later, which is a mistake.
First off, when it comes to the pedigree score, the large number on your pet you see is the summation of all the talent scores your pet has available to it to draw from. A high pedigree score may not be as good as a lower pedigree score in some instances as two pedigree talents are often targetting, damage increase, health increase, and the like while three pedigree talents often are stuff that increases a pets max ability limits which may not be at all useful to you.
The smaller number you see is the sum of your learned talent scores, and once again higher point totals aren't necessarily better.
When it comes to pets, for your in game playing pet you basically want a pet that will improve your character's abilities and gives a helpful card. A second pet is usually nice to have for pet racing, on this one you merely want high max abilities and good racing talents.
When it comes to games you should play those you can easily get maximum training points from. I am only good at the maze and the dance game. On the dance game I boost my strength and my agility. On the maze game I boost my strength, intellect, and will. I then feed my pets the foods I've found during normal play to max out all pet stats.
Pets who are babies cost two pet points to train. Teens four points. Adults six points. Ancient eight points. Epic eight points (necessary to continue to train if your last talent drawn increased a max ability limit). You normally max out all max limits long before your pet ever hits epic so reaching maxes isn't anything much to worry about.
Every time your character levels up after it is first able to train pets (I think it is at level 7 you can train), your pet ball fills up. It is therefore essential to empty your pet ball right before leveling up, and then empty it right after leveling up, and then empty it whenever it is close to maxing out or before you log off.
You are allowed six character slots, so you can use the characters you have but aren't currently playing to hold other pets, then you can go from character to character and level up pets all at once. Moving a pet from one character to another empties the pet ball of the one taking it out of the chest, so you can't take advantage of such transfers.
If you press escape on a game that you are messing up on you do not lose any points and can play another game. I do this all the time to insure I get the most pet training points from the game as possible.
If you want to mix a pet you need to get it to adult. Some pets don't get their pet cards until ancient or epic so if you want that pet's card you will have to get it there. Otherwise, if a pet draws talents that simply aren't useful to you, and you don't plan to mix the pet then you should simply stop training it and find another pet that will hopefully benifit you. Any pet type can become a high pedigree pet if you mix it enough times with high pedigree pets and always recieve its pet type from the eggs.
The best pets for you and the best pet mixes for you are typically always the ones that benifits your character in terms of your schools. So when you pay gold to mix pets, ask yourself if mixing such pet types will likely help you or not if you are lucky enough with their random talent draws.
Pets that don't work out simply become show pets that you place into your home.
Ravens are a very good place to farm to get gold for mixing pets with.