According to your profile here you've already got ~240 pets leveled up to 25 so I assume you've got all the useful ones leveled and have your teams for the trainers, CT, etc. Beyond that it's just really what ever order you want. Personally, I did a variety of things while working my way towards all level 25 pets to keep myself interested. For example:
Leveling all my undead or dragonkin pets. Works well for families with fewer pets but I wouldn't recommend doing beasts or critters this way.
Leveling all my spiders or roaches.
Leveling all my pets captured in a specific zone.
I also worked on upgrading my wild pets to rares starting in the highest level zones so that the pets I caught were already higher level and so that I could be getting some experience in the process.
Pretty much any way of breaking it down into a smaller group so I felt like I had accomplished something rather than just a small piece of a huge task.
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