2. Raise more than one set at a time. You'll need more than 3 because no team is strong against everything.
3. Use strats that exploit not only your enemies weakness but a strength against their main attack type. All strength and weaknesses can be found on WoWpedia.
4. Mechanical, humanoid, and "something with heals" is the easiest combo to level.
A) Mechanical is strong against beasts and a lot of the wild battles will have beasts. Mechanical types also have repair which is very handy.
B) Humanoids are strong against critters, this goes for double when the humanoid has beast type attacks because critters are weak against beasts. They also heal after every turn that they do damage on.
C) "Something that heals" This is where the Fawn, Emerald Whelp, Restless Shadeling come in. They have heals or debuffs that heal your party and help keep 'em topped off. This is good for rough fights where you need to outlast the enemy, capturing where you need to survive a fight until you can nab the pet, or healing to avoid down time on the pet revive and keep on leveling.