4. You can make PokeCoins daily without buying them
There is a button in the PokeStore in the upper right corner that looks like a shield. This button has a 21 hour cooldown. When it is on cooldown and you press it, for every Pokemon you have in ANY gym you will receive 100 dust and 10 PokeCoins.
The best use of this is to find an area with multiple gyms in a small area, get some teammates together to take them down, and then immediately hit the button. 20-30 Pokecoins daily is an easy goal.