The Cost of Your Pet
Don't feed your pet. It takes up unnecessary money, and if you go to the healing springs enough, it'll get fed. You pet won't die. Even if it's miserable, playing with it takes up time too.
If you battle, then yeah, increase its levels (though this is expensive, especially later). However, feeding and playing with it takes up money and time. Both of which cost you money.
Even if your pet is dying of something, just go to the healing springs. Never buy medicine, but really, your pet won't die, so who cares.
Something related to this is the cost of you. I found the reason most people are "poor" is because they spend too much. They want that newest plushie, or they want a gallery of ____ or they want to buy every paint brush in existence. If you aren't going to buy it to sell it, you are essentially losing that money.
Yeah, you didn't "lose" the money, but if it's tied up in at item that is never going to be sold, you essentially lost that money. This is fine when you have like 5 million points, but not good when you only have like 1-2 million. You want to stay liquid. I'll cover that in the next one, Stay Liquid.