Battling Is a great way to earn TC on the site, and almost one of the fastest ways.
One of the best ways of getting training potions would be to save up lots of TC, then posting on the sell it or buy it board, "looking to buy the training potions In bulk". But you have to be careful on witch ones you buy, and you always have to keep your level up. Good weapons also help along with defeating tough opponents. High stats are good, but sometimes having a good stated weapon could be even more helpful.
But you must be patient, training takes time.
Potions;
Blood Potion
One of the most expensive of the training potions.
It trains your pets strength.
Silver Potion
Also another expensive potion.
It trains your pets defense
Earth Potion
It trains your pets level.
Stamina Potion
It trains/raises your pets stamina.
Mystery Potion
It trains/raises your pets magic.
Buying these potions may be a challenge, so check back often at the potion shop.
Remember to always train your pets level up!